Apparatus and Methods For Nanoparticle Generation and Process Intensification of Transport and Reaction Systems

ABSTRACT

Apparatus, systems and methods are provided that utilize microreactor technology to achieve desired mixing and interaction at a micro and/or molecular level between and among feed stream constituents. Feed streams are fed to an intensifier pump at individually controlled rates, e.g., based on operation of individually controlled feed pumps. The time during which first and second feed streams are combined/mixed prior to introduction to the microreactor is generally minimized, thereby avoiding potential reactions and other constituent interactions prior to micro- and/or nano-scale interactions within the microreactor. Various microreactor designs/geometries may be employed, e.g., “Z” type single or multi-slot geometries and “Y” type single or multi-slot geometries. Various applications benefit from the disclosure, including emulsion, crystallization, encapsulation and reaction processes.

TECHNICAL FIELD

The present disclosure is directed to apparatus, systems and methodsthat facilitate highly effective molecular contact/interaction within adefined reaction chamber, thereby enhancing and/or promoting a host ofmixing and/or reaction phenomena. More particularly, the disclosedapparatus, systems and methods are designed to bring togetherconstituent streams for interaction within a defined reaction chamber soas to achieve highly desirable results.

BACKGROUND

The role of hydrodynamics should not be underestimated in any facet ofthe engineering sciences. The flow patterns within process units andtheir associated transfer lines have a significant impact upon mass,energy and momentum transport rates and reaction proficiency. Thus,system designs generally benefit from the identification of energydissipation mechanisms and, thus, quantification of the intensity ofmixing and contact efficacy. These are generally important factors inmaterials handling and manufacturing processes.

For example, the intensity of turbulence generally influences the sizeof particles that are dispersed throughout a fluid, the quality of anemulsion, and the residence time distribution profiles that determineprogress and selectivity of chemical reactions. This is particularlyapparent in the emerging nanotechnologies, where precipitation andcrystallization processes have a significant impact on product quality.Furthermore, mixing characteristics influence and/or determine theperformance of reaction vessels, at both laboratory and productionscales, and properly designed/implemented mixing systems can permitand/or facilitate the use of continuous systems, in lieu of batchsystems, to enhance productivity.

In terms of mixing technologies, cavitation has been used in industryfor homogenization operations, i.e., to disperse suspended particles incolloidal liquids. Numerous engineering principles are involved withcavitation behavior (see, e.g., Christopher Earls Brennen, “Cavitationand Bubble Dynamics”, Oxford University Press (1995)). Althoughcavitation-based mixing is often employed with solids, it may not be thebest choice for generation of nano emulsions and vesicle loading, as indrug chaperones. Cavitation can result in issues associated withmaterials of construction and/or scale-up issues for mixing devicefabrication. In particular, by forcing a liquid through an annularopening that has a narrow entrance orifice with a much larger exitorifice, a dramatic decrease in pressure results in fluid accelerationinto a larger volume and generation of cavitation bubbles. The surfaceupon which these bubbles collide (causing their implosion) is subjectedto tremendous stresses. Thus, materials such as polycrystalline diamondand stainless steel are generally required.

Beyond mixing-related issues, a large number of compounds withpotentially high pharmacological value fail to pass initial screeningtests because they are too hydrophobic to be effectively formulated.Most formulation strategies aim at increasing the bioavailability ofsuch drugs by particle size reduction, as described extensively in theliterature. Such strategies include the production of emulsions,liposomes and functionalized chaperones by high shear processing, theproduction of nanosuspensions by milling, micronization or high shearprocessing, and the production of nanoporous materials.

Nano-emulsions, liposomes and other generalized cargo loaded systems canonly encapsulate a limited amount of drug. Therefore, current approachesmay not be the strategies of choice for drugs with high dosage demands.Nanosuspensions can deliver much larger amounts of drug in a smallervolume than solvent-diluted drug systems and, therefore, have apotential advantage as a formulation strategy.

Most often, nanosuspensions are produced by milling, micronizing or highshear processing. Thus, current methods for manufacturingnanosuspensions primarily rely on the reduction of particle size of drugpowders in dry or wet formulations. Such “top-down” processes aregenerally slow, require repetitive processing cycles, and requiresubstantial energy. Indeed, the targeted particle sizes, usually lessthan 0.5 microns, are often time consuming and expensive to produce,frequently requiring repetitive processing cycles/passes through themilling/high shear equipment to achieve desired particle sizedistributions.

Controlled crystallization of drugs is an alternative to the productionof drug nanosuspensions through size reduction techniques for generatingdesired particle size distributions. Crystallization is a method that isused to produce fine chemicals and pharmaceuticals of desired purityand/or for the formation of a specific crystal polymorph with desiredcrystalline structure and associated properties. However, currentcrystallization techniques typically produce particles in the range ofseveral microns which are not suitable for delivering highly hydrophobicdrugs. More recently, methods for production of nanosuspensions throughcrystallization have been proposed, but they have not demonstrated thenecessary productivity robustness. In particular, the newer procedureslack the control that is required at the various mechanistic steps ofcrystallization (nucleation rate through crystal morphology andstabilization), process scalability and general applicability.

The patent literature describes processing equipment for particle sizecontrol and manipulation. For example, commonly assigned U.S. Pat. Nos.4,533,254 and 4,908,154 to Cook et al. describe processing systems andapparatus having particular utility in emulsion and microemulsionprocessing. Flow streams are forced under pressure to impinge in alow-pressure turbulent zone. The disclosed systems/apparatus include aplurality of nozzles that effect impingement of flow sheets along acommon liquid jet interaction front.

More recently, commonly assigned U.S. Pat. Nos. 6,159,442 and 6,221,332to Thumm et al. describe multiple stream, high pressure continuouschemical mixers/reactors that are adapted to: (i) individuallypressurize different liquid streams to high pressure: (ii) individuallymonitor the flow of each liquid stream; (iii) provide a reaction chamberfor receiving the pressurized liquid streams at high velocity; (iv)discharge a product stream which results from mixing of the pressurizedliquid source material streams at high pressure and high velocity in thereaction chamber; and (v) control the rate of delivery of each reactantstream to the reaction chamber at a determined continuous stoichiometricrate. The Thumm et al. patents further disclose a closed loop controlsystem that combines individual stream transducers to allow calculationof flow of each stream, computer hardware with control systemapplication software, a hydraulic pressure/flow metering valve for eachstream, and input/output connections to the computer hardware for thetransducer data and meter valve drive. Of note, Thumm et al. contemplatepressurizing each reactant stream with a hydraulically-drivenintensifier, wherein hydraulic pressure-flow metering valves regulatethe intensifier's drive, thereby regulating the pressure and flow ofeach reactant stream.

Beyond the commonly assigned patent filings noted above, reference ismade to the following patents/patent publications. Greenwood et al.disclose a sterilizable particle-size reduction apparatus in WO2005/018687. Kipp et al. disclose methods/apparatus for generatingsubmicron particle suspensions that involves mixing a solution thatcontains a pharmaceutically active compound that is dissolved in awater-miscible solvent with a second solvent to form a pre-suspension ofparticles and then energizing the mixture to form a particle suspensionhaving an average particle size of less than 100 μm (see U.S. PatentPublications 2003/0206959 and 2004/0266890; U.S. Pat. No. 6,977,085).

In the field of crystallization, the patent literature includes variousteachings from the pharmaceutical industry. For example, U.S. Pat. No.5,314,506 to Midler, Jr. et al. discloses the use of impinging jets toachieve high intensity micromixing of fluids so as to form a homogeneouscomposition prior to the start of nucleation in a continuouscrystallization process. Nucleation and precipitation are initiated byutilizing the effect of temperature reduction on the solubility of thecompound to be crystallized in a particular solvent (thermoregulation),or by taking advantage of the solubility characteristics of the compoundin solvent mixtures, or a combination thereof. U.S. Pat. No. 5,578,279to Dauer et al. discloses a dual jet crystallizer apparatus thatincludes a crystallization or mixing chamber having opposed angularlydisposed jet nozzles. The nozzles deliver the compound to becrystallized and a crystallization agent. U.S. Pat. No. 6,558,435 to AmEnde et al. discloses a process for synthesis/crystallization of apharmaceutical compound that involves contacting diametrically opposedliquid jet streams, such that the liquid streams meet at a point ofimpingement to create a vertical impingement film and create turbulenceat their point of impact under conditions of temperature and pressurewhich permit reaction of reactive intermediates to produce a product.The jet streams are disclosed to have sufficient linear velocity toachieve micromixing of the jet stream constituents, followed by reactionand nucleation to form high surface area crystals. See also U.S. PatentPublication No. 2006/0151899 to Kato et al.

Despite efforts to date, a need remains for systems/apparatus andmethods that are effective in producing nanoparticles. Systems/apparatusand processes for generation of nanoparticles in an efficient,continuous and reliable manner are also needed. Beyond nanoparticleprocessing, there remains a need for systems/apparatus and methods thatare effective in facilitating various materials processing operations,e.g., reaction, emulsion and/or crystallization processes, by, interalia, minimizing diffusion limitations to requisite interaction betweenreactants and/or crystallizing constituents. Still further, a needremains for systems and methods that yield desirable particle sizedistributions, morphology and/or compositions/phase purities througheffective process design and/or control. Indeed, a need remains forsystems and methods that effectively control interfacialreaction/contact between constituents to achieve desired processingresults, e.g., to reduce the potential for undesirable side reactions.These and other needs are satisfied by the disclosed systems/apparatusand methods.

Summary

Micro-scale apparatus, systems and methods are provided according to thepresent disclosure that facilitate and utilize microreactor technologyto achieve desired mixing and interaction at a micro and/or molecularlevel between and among feed stream constituents. The disclosedapparatus, systems and methods are capable of various degrees of mixingintensity and control of energy dissipation mechanisms, therebymaximizing useful work in forming surfaces and interfaces between andamong constituent molecules/compounds. The present disclosure permitsadvantageous reductions in system entropy that might be otherwiseexperienced due to process inefficiencies. Such entropy reduction is amajor benefit standing alone, but also translates to minimizing energylost to heat, sound, light and cavitation. Indeed, reduced systementropy advantageously further translates to a reduced propensity forcomponent damage.

Furthermore, the disclosed apparatus, system and methods advantageouslyfacilitate and/or support process intensification, thereby miniaturizingunit operations and processes through both scale reduction andintegration of operational steps, e.g., reaction and separation unitoperations. Consequently, processes utilizing the disclosed apparatus,systems and methods offer enhanced efficiency and cost effectiveness. Inaddition, exemplary embodiments/implementations of the disclosedapparatus, systems and methods are adapted to function in environmentsthat require portability, thereby providing enhanced flexibility inapplications and in-use time.

Key design features exploited according to the present disclosure permitcontrol of the amount and form of energy dissipation that occurs atspecific locations in the system, particularly the interaction chamberof the disclosed apparatus/systems. High energy input is generallyaccomplished using intensifier pumps. Narrow flow channels convertenergy input from the intensifier pumps to high fluid velocities(kinetic energy) and associated shear rates. The individual jets can becreated in a number of ways, using advantageous feed system designs thatminimize, and in some cases eliminate, premixing events. According to anexemplary embodiment of the present disclosure, multiple jet streamsimpinge upon each other in an interaction chamber, where controllableintimate contacting is accomplished. In other exemplary embodiments,intimate contact between constituent streams/molecules may be achievedthrough shear-based flow designs, e.g., Z-type flow channels. Dependingupon the energy dissipation rate, various degrees of mixing intensity(i.e., macro-, meso-, or micro-mixing) and associated levels ofturbulence intensity (i.e., eddy sizes) are obtained. In exemplaryimplementations of the present disclosure, the size of the smallesteddies formed, and thus the Kolmogorov scale for the desired diffusionand reaction coordinates, are in the 50-200 nanometer range.

Exemplary apparatus/systems of the present disclosure include at leasttwo feed streams. The feed streams are advantageously fed to anintensifier pump at individually controlled rates, e.g., based onoperation of individually controlled feed pumps. In exemplaryembodiments, the feed pumps are peristaltic pumps that are adapted tometer the flow of the individual feed streams at desired relative rates.Alternative feed pump designs may be employed, e.g., gear pumps,provided flow control is permitted. In this way, various feed ratios maybe achieved. Indeed, through feed pump adjustments, the disclosedapparatus/system facilitates wide ranging variations in feed ratios,thereby permitting and/or supporting various reaction, crystallizationand other processing schemes. Of note, one or more recycled streams maybe combined with such feed streams as they are fed to or within thedisclosed intensifier pump.

The first and second feed streams may be fed from the first/second feedpumps to the intensifier pump in independent feed lines that arecombined prior to pressurization by the intensifier pump. Alternatively,the feed streams may flow to the intensifier pump in a coaxial manner.Thus, a first feed stream may flow through a first pipe/line that ispositioned coaxially within a second pipe/line. Coaxial combination ofthe first and second feed lines is achieved through appropriate pipefitting, as will be apparent to persons skilled in the art. In eithercase, systems and methods of the present disclosure generally benefit byminimizing the time during which the first and second feed streams arecombined/mixed prior to introduction to the disclosed interactionchamber. Indeed, the present disclosure advantageously places themicroreactor in close proximity to feed stream intensification. In thisway, potentially undesirable reactions and/or other constituentinteractions are minimized prior to the point in time when suchinteractions can occur at the micro- and/or nano-scale, therebyenhancing phase purity and/or selectivity of the disclosed systems andmethods.

The intensifier pump is generally effective to pressurize the first andsecond feed streams to an elevated pressure, e.g., a pressure of up to40,000 psi. As used herein, the term “intensifier pump” refers to a highpressure pump that is adapted to deliver high pressure output streams,e.g., 500 to 40,000 psi and higher. An exemplary intensifier pumpincludes an hydraulic pump and a piston that multiplies the systempressure therewithin. Thus, the hydraulic pump may be effective togenerate pressures of about 1500 to 3500 psi, and the piston mechanismmay be effective to multiply such pressure by a factor of 10× to 30×. Ofnote, each piston within a pressure assembly may be viewed as a distinctintensifier pump for purposes of the present disclosure. Exemplaryintensifier pumps according to the present disclosure avoid cavitation,thereby minimizing potential energy dissipation associated therewith.

In exemplary embodiments, individual feed streams are introduced to anintensifier pump at axially-spaced ports, thereby permitting effectivepressurization of such feed streams while limiting potential pre-mixingof constituents prior to introduction to the microreactor. Thus,exemplary intensifier pumps include a plurality of ports with associatedpiping/tubing for introduction of individual feed streams along theaxial flow path of the intensifier pump.

The pressurized stream is then fed to an interaction/reaction chamber,i.e., a microreactor, for interactive contact. The interaction/reactionchamber may be characterized by various geometries. Thus, in exemplaryembodiments of the present disclosure, the interaction/reaction chambermay take the form of (i) a “Z” type single slot geometry, (ii) a “Y”type single slot geometry, (iii) a “Z” type multi-slot geometry; or (iv)a “Y” type multi-slot geometry. The interaction/reaction chambergenerally defines an internal volume that is on the scale of amicroliter, and average velocities in the microchannels may reach 500m/s. Changes in velocity magnitude and/or direction associated with thedisclosed interaction/reaction chambers yields substantially uniform,high shear fields. The high turbulence achieved in the disclosedinteraction/reaction chambers advantageously facilitates mixing/contactat the nanometer level.

Various downstream units and/or operations may be provided according tothe present disclosure. For example, a cooling jacket or other heatexchange unit may be provided to cool the fluid stream after exiting theinteraction/reaction chamber. Recycling of a portion of such outletstream to the intensifier pump inlet may also be provided, e.g., tofacilitate further reaction/crystallization of constituents.

As noted above, the disclosed systems/apparatus are advantageouslyadapted to control interaction of constituents at a non-nanoscale level.In exemplary embodiments, such control is achieved by providing (i) afirst feed line for introducing a first constituent to an intensifierpump, a second feed line for introducing a second constituent to theintensifier pump; and an interaction chamber/microreactor downstream ofthe intensifier pump, the interaction chamber/microreactor being adaptedto effect nanoscale interaction between the first constituent and thesecond constituent. The first feed line may be coaxially positionedwithin the second feed line so as to control mixing of the first andsecond constituents prior to pressurization by the intensifier pump.Alternatively, the first feed line may direct flow to a firstintensifier pump port, while the second feed line may direct flow to asecond, axially-spaced intensifier pump port. In this way, theopportunity for the constituents to interact prior toprocessing/interaction within the interaction chamber/microreactor,i.e., at a non-nanoscale level, is effectively inhibited and/orsubstantially prevented.

The disclosed apparatus, systems and methods make it possible toovercome the limitations of prior art systems through precise control ofenergy input and dissipation mechanisms that dictate/control processpathways and rates. For example, in an exemplary implementation of thepresent disclosure, solvent composition may be used to affectsuper-saturation conditions, e.g., through addition of a miscible nonsolvent. In further exemplary implementations of the present disclosure,a process/method is provided that employs a solvent/anti-solventcrystallization technique in conjunction with the disclosedapparatus/system to produce advantageous drug nanosuspensions. Ascompared to micro-mixing models reported in the literature, turbulentenergy dissipation rates attainable in the disclosed interactionchambers/microreactors are on the order of 10⁷ W/kg and higher. Thedisclosed apparatus/system thus achieves rapid micro-mixing (time scale4 μs) and meso-mixing (time scale 20 μs), with a nominal residence timein the interaction chamber that is on the order of 1 ms. In addition,mixing at the nanometer scale provides a uniform supersaturation ratiowhich is a major controlling factor in crystal formation and growth.Controlling the timing and location of the mixing of the solvent andanti-solvent streams provides control of the onset of the nucleationprocess. This control, in combination with a homogeneous supersaturationratio, results in desirably uniform crystal growth and stabilizationrates.

Numerous processes may benefit through use/implementation of thedisclosed apparatus and systems. In particular, process implementationsbenefit, at least in part, based on an ability to maximize the degree towhich input energy is desirably directed to forming/establishinginteraction surfaces and interfaces. Turbulence and surface tensionforces achieved according to the present disclosure are advantageouslyeffective in initiating nano-scale events, such as formation of stablenano-emulsions and formation of sufficient molecular clustering tocreate/establish homogeneous nucleation sites for crystal growth.Exemplary applications/implementations of the present disclosure alsoinclude, but are not limited to, selectivity enhancement in competitivereaction networks, control of size of dispersed solids (whether fromreactive precipitation, crystallization and/or declustering), control ofcrystalline drug polymorph selectivity, and formation of chaperonesystems via encapsulation of active ingredients.

Thus, the present disclosure provides exemplary apparatus/systems andmethods that facilitate direct impingement of jet streams in acontinuous, impinging jet microreactor scalable to at least 50 litersper minute, thereby generating a high level of energy dissipation perunit volume. This energy generation results in intimate contact of thecomponents/constituents in the jet streams. By controlling the velocityof these streams, the present disclosure may establish various levels ofmixing scales (i.e., macro-, meso-, and micro-mixing), which translateand/or correspond to varying length scales of turbulent eddies. Thesmallest eddies establish the minimum length scales at which moleculardiffusion processes occur between the jet stream components/constituentswhich, in turn, establish time scales for phenomenological events totake place. As such, the selectivity in competing reaction networks maybe controlled by generating high local concentration gradients of thedesired reactants. In alternative implementations, direct jet streamimpingement is replaced by high shear microreactor designs, e.g., Z-typechannels, that achieve comparable levels of intimate contact/mixing.

The foregoing phenomena are important parameters for reactions/systemsthat are limited and/or controlled by mass transfer rates/performance.Thus, the present disclosure advantageously facilitates formation ofcritical sized clusters that become homogeneous nucleation sites forcrystal growth via high degrees of local super-saturation. Suchnucleation sites influence the molecular diffusion processes formingsurfaces, their growth rates, integration of various molecular speciesinto the surface, and ultimate size and purity of the particles formed.

The foregoing molecular species may form various polymorphs, and thedesired form can be obtained through manipulation of operationalparameters, e.g., microreactor design, microreactor geometry, pressuregenerated by the intensifier pump, supersaturation ratio, solvents,antisolvents, temperature and combinations thereof. Mass transferlimitations in multiphase reacting systems can be overcome according tothe present disclosure, e.g., in the production of biodiesel, becausethe liquid reactants have limited solubility in each other and,therefore, an interfacial reaction must occur during an initial “lagphase”. The rate of such interfacial reaction may be enhanced bydispersing small droplets of one phase into the other, greatly improvingthe interfacial surface area to volume ratio.

The same phenomenon is noted when heterogeneous reactions involvingsolid particles are involved. In particular, a surface-to-volumeenhancement accelerates turnover rates proportional to surface areaavailability, whether the surface is catalytic or a reactant. Moreover,boundary layer resistances are reduced as particle size is reduced, onceagain promoting reaction rates up to their fundamental/intrinsic rates.This phenomenon is also applicable when interfacial mass transfer limitsdownstream separation processes, e.g., for downstream extraction,absorption, and adsorption processes, and for formation of stableemulsions, with or without surface active agents, since droplets at nanoscale sizes, although thermodynamically unstable, can exist for lengthytime scales due to an extremely slow kinetics response.

Chaperone systems, such as with immiscible fluids or isolationrequirements from the continuous phase (as in targeting for imagingand/or drug delivery) are readily prepared via the present disclosureusing surface active agents as the encapsulate and, due to minimizationof potential heat effects while processing vesicles, heat liable surfaceactive agents, such as those with protein functionality, can beutilized. Of note, the high shear forces associated with the disclosedinteraction chambers can be beneficial when shear thinning or thickeningbehavior is to be exploited during processing.

In addition, the present disclosure facilitates encapsulation down tothe nano-scale of hydrophobic substances within amphi-morphicsurfactants for dispersion in hydrophilic environments (or vice versa),as in nutraceutics, pharmaceutics, and cosmetics. The encapsulates canalso be useful in functionalizing membranes and providing “smart”characteristics; for example, as (a) sequestering agents in guardsystems, (b) controlled release of growth factors in tissue engineeringapplications, (c) soluble gas transport enhancement, and (d) in generalsensor/recorder systems. The disclosed apparatus/systems and methods maybe used to facilitate both fast and slow processes, and to facilitatechemical reactions and physical processes, such as crystallization.

Further, the present disclosures advantageously facilitates productionof polymer nanosuspensions in the range of 50-500 nm using both emulsionand precipitation methods. By controlling processing parameters,nanosuspensions with various polymer sizes and densities may be created.The disclosed systems/methods may be used to provide activepharmaceutical ingredients (API's) that are encapsulated or otherwisecontained within a polymeric matrix. In this sense, the polymeric matrixfunctions as a “chaperone” for such API's. The polymeric matrix isgenerally amorphous and may advantageously define a biocompatible and/orbioabsorbable product. The feedstream for such processing techniques mayinclude monomeric constituents, polymeric constituents or combinationsthereof.

Additional advantage features, functions and implementations of thedisclosed apparatus, systems and methods will be apparent from thedescription which follows, particularly when read in conjunction withthe appended figures.

BRIEF DESCRIPTION OF THE FIGURES

To assist those of ordinary skill in the art in making and using thedisclosed apparatus, systems and methods, reference is made to theaccompanying figures, wherein:

FIG. 1 is a schematic depiction of an exemplary system for processing oftwo liquid/reactant streams according to the present disclosure;

FIGS. 2A and 2B are schematic depictions of a further exemplary systemfor processing liquid reactant streams according to the presentdisclosure, wherein two streams are mixed immediately prior tointroduction to an intensifier pump;

FIGS. 2C and 2D are schematic depictions of an additional exemplarysystem for processing liquid reactant streams according to the presentdisclosure, wherein two streams are independently introduced to separateports formed in an intensifier pump;

FIG. 3 is a schematic depiction of an exemplary opposed jet reactionchamber;

FIG. 4A is a schematic depiction of an exemplary feed streamimplementation that includes hydraulic-based control according to thepresent disclosure;

FIG. 4B is a schematic depiction of an exemplary feed streamimplementation that includes a recycled reactant/stream according to thepresent disclosure;

FIG. 5 is a graph depicting solubility of Norfloxacin (NFN) indimethyl-sulfoxide (DMSO) and water solution as a function of watercontent and corresponding percentage of NFN that precipitates from theinitially saturated NFN/DMSO solution;

FIG. 6 is a graph depicting particle size distribution of a NFNsuspension produced in experimental tests according to the presentdisclosure;

FIG. 7 is an SEM image of a NFN suspension produced in experimentaltests according to the present disclosure;

FIG. 8 is a graph depicting the median particle size of NFN as afunction of processing pressure for experimental tests run according tothe present disclosure;

FIG. 9 is a graph depicting median particle size of NFN dispersions as afunction of NFN concentration in DMSO for experimental tests runaccording to the present disclosure;

FIG. 10 is a graph depicting particle size as a function ofsupersaturation ratio at 138 MPa process pressure for experimental testsrun according to the present disclosure;

FIG. 11 is a graph depicting process efficiency as a function ofsupersaturation ratio at 138 MPa process pressure for experimental testsrun according to the present disclosure;

FIG. 12 is a graph depicting the effect of surfactant on particle sizedistribution of particles from an exemplary recrystallization experimentaccording to the present disclosure;

FIGS. 13A and 13B are SEM images of control crystals produced accordingto experimental runs, wherein FIG. 13A shows NFN particles grown in a noshear environment (100×) and FIG. 13B shows those same crystals afterbeing reduced using standard Microfluidizer® technology (30 passes at30,000 psi; 1000×);

FIG. 14 shows diffraction patterns for samples that were crystallizedusing the DMSO/water solvent/anti-solvent system in experimental runs;

FIG. 15 shows diffraction patterns for NFN as purchased;

FIG. 16 is a TEM image of azythromycin particles produced with thedisclosed apparatus/system;

FIG. 20 is a schematic depiction of a reaction scheme for biodieselsynthesis;

FIG. 21 is a schematic depiction of a system wherein two phases aresimultaneously mixed;

FIGS. 22A and 22B are schematic depictions of a system wherein phasesare independently agitated in sequence;

FIG. 23 is a schematic depiction of a system wherein both phases arenon-agitated;

FIG. 24 is a TEM image of polymer nanoparticles generated according toan exemplary implementation of the present disclosure;

FIG. 25 is an SEM image polymer nanoparticles generated according to anexemplary implementation of the present disclosure; and

FIGS. 26A and 26B are optical microscope images that included polymerand API (FIG. 26A) and API only (FIG. 26B).

DESCRIPTION OF EXEMPLARY EMBODIMENT(S)

The present disclosure provides advantageous apparatus, systems andmethods for achieving effective contact/interaction of constituentswithin a defined chamber, i.e., an interaction chamber or microreactor,to enhance and/or promote a host of mixing and/or reaction phenomena.Set forth herein below are descriptions of exemplary apparatus/systemdesigns and implementations, including exemplary implementations andbeneficial results achieved thereby. Although the apparatus, systems andmethods of the present disclosure are described with reference toexemplary embodiments and implementations, it is to be understood thatthe present disclosure is not limited to such illustrative examples.Rather, the disclosed apparatus, systems and methods may take variousphysical forms and be applied to a multitude of processing schemes andenvironments, without departing from the spirit or scope of the presentdisclosure.

A. Exemplary Apparatus/System Design(s)

Exemplary apparatus/systems according to the present disclosure aregenerally designed to accommodate the interaction of two or more liquidstreams, e.g., reactants. The two or more liquid streams are generallypumped to an intensifier pump by individual feed pumps. The disclosedapparatus/systems are designed such that the liquid streams arecombined/mixed in a controlled ratio, in a controlled location, and withcontrolled energy input.

With initial reference to FIG. 1, two exemplary liquid streams(“Reactant 1” and “Reactant 2”) are schematically depicted as part of aprocessing arrangement according to the present disclosure. Theliquids/reactants may take various forms and exhibit various propertiesaccording to the present disclosure, e.g., they may be multiphasefluids, miscible fluids and/or immiscible fluids. The reactants aredepicted in connection with feed vessels/reservoirs. Of course, themanner in which the liquid streams are processed and/or stored prior tointroduction to the disclosed processing apparatus/system may varywidely, with the disclosed reactant reservoirs being merely illustrativeof pre-processing handling/storage of reactant/fluid streams. Thereactants are generally combined in connection with an intensifier pumpor other high pressure pump, so as to pressurize such combined reactantstream (e.g., to pressures up to 40,000 psi) for feed to an interactionchamber.

Of note, the exemplary apparatus/system that is schematically depictedin FIG. 1 includes a coaxial feed feature/design for delivery of thereactants to the intensifier pump. In this regard, the feed line/pipefor a first reactant, e.g., Reactant 1, may be positioned within thefeed line/pipe for a second reactant, e.g., Reactant 2, such thatdelivery of such reactant streams to the intensifier pump (or other highpressure pump) is substantially coaxial. Thus, the feed line/pipe forthe second reactant may define a larger internal/diameter as compared tothe outer diameter of the feed line/pipe for the first reactant, therebypermitting flow of the second reactant in a ring-shaped flow channeldefined around the exterior of the feed line/pipe for the firstreactant. In this way, mixing between the first and second reactants isavoided (or substantially minimized) until immediately prior to pressureintensification. Accordingly, premature interaction between the firstand second reactants is advantageously avoided and interaction betweensuch reactants occurs in the interaction chamber/microreactor, e.g., atthe nanoscale level. Alternative flow patterns may be employed, e.g.,side-by-side feed lines/pipes, to minimize/prevent premature interactionand/or mixing without departing from the spirit or scope of the presentdisclosure.

The feed pump(s) in combination with the intensifier/high pressure pumpcontrol the flow rate ratios of the two streams. The energy input to thefluid at different locations of the system is controlled by the geometryof the flow path. Thus, energy dissipation may be controlled/minimizedthrough advantageous piping design/layout, the design/geometry of theinteraction chamber/microreactor, and the design/layout of heatexchanger positioned downstream of the interaction chamber. Typically,energy dissipation is most strongly influenced by the design/geometry ofthe interaction chamber/microreactor, e.g., through turbulence and/orshear associated therewith.

The liquid/reactant streams advantageously interact inside the fixedgeometry interaction chamber/microreactor at the nanometer scale.Downstream of the interaction chamber/microreactor, the combined liquidstream is typically fed into a heat exchanger where it is cooled orheated (if desired). Of note, the liquid may be collected, in whole orin part, at this processing stage. However, in exemplaryembodiments/implementations of the present disclosure, the liquid streamis recycled to the apparatus/system, in whole or in part, e.g., throughintroduction of a recycle feed upstream of the intensifier pump/highpressure pump.

With reference to FIGS. 2A-2D, exemplary flow implementations accordingto the present disclosure are schematically depicted. Thus, with initialreference to FIGS. 2A and 2B, an hydraulic pump is powered by a motor soas to deliver hydraulic oil to an intensifier pump. First and secondfeed streams are combined immediately prior to introduction to theintensifier pump (see FIG. 2B) and the combined stream is pressurizedfor delivery to a reaction chamber. Upon exiting the reaction chamber,the combined stream enters a heat exchanger for temperature control(i.e., cooling or heating). Of note, the first and second feed streamsmay be combined in a manifold, tee or the like prior to introductionthrough a port into the intensifier pump.

Turning to FIGS. 2C and 2D, an alternative exemplary fluiddelivery/intensifier pump design is schematically depicted. Theintensifier pump defines a plurality of ports for introduction ofindividual fluid streams thereto. As schematically depicted in FIG. 2D,the ports may be oriented on opposite sides of a chamber defined by theintensifier pump. The ports may also be axially spaced relative to thefluid flow path through the intensifier pump (whether on the same oropposite sides thereof), such that individual feed streams areintroduced to the intensifier pump at distinct axial locationstherewithin. In the schematically depicted embodiment of FIGS. 2C and2D, two distinct ports are provided with respect to intensificationpump—one port for receipt/delivery of a first reactant stream and asecond port for receipt/delivery of a second reactant stream—butadditional ports may be provided (e.g., additional axially-spaced and/orperipherally-spaced ports). Thus, for example, further ports may beprovided in connection with the disclosed intensifier pump forreceipt/delivery of a recycle stream, a further reactant stream and/orprocessing stream (e.g., a surfactant stream), and/or portions of thereactant streams introduced to the first and/or second depicted ports.By providing distinct feed ports (e.g., axially-spaced and/orperipherally-spaced ports) in connection with the disclosed intensifierpump, the apparatus/system of the present disclosure is advantageouslyadapted to further minimize the interaction/contact between individualfluid/reactant streams prior to introduction to the downstreammicroreactor.

FIG. 3 provides a schematic depiction of an exemplary opposed jetreaction chamber. The geometry of the interaction chamber/microreactormay take various forms to effect the desired shear field and/or shearforce. For example, the interaction chamber may be characterized by (i)a “Z” type single slot geometry, (ii) a “Y” type single slot geometry,(iii) a “Z” type multi-slot geometry; or (iv) a “Y” type multi-slotgeometry. Each of the foregoing interaction chamber/microreactorgeometries is known in the art and is generally adapted to provide ahigh shear field for interaction between the reactants/constituentsintroduced thereto. The disclosed interaction chambers/microreactors aregenerally effective to generate nanoscale mixing, tight particle sizedistributions, and high levels of repeatability/scalability.

As schematically depicted in FIGS. 4A-4B, the intensifier pump generallyincludes a hydraulic system for generating the high pressures associatedwith the disclosed apparatus/system. Thus, the hydraulic systemtypically includes a motor that drives a hydraulic pump for pressurizinghydraulic fluid, e.g., hydraulic oil, for delivery to the intensifierpump. The hydraulic oil flows into and through the intensifier pump,delivering the requisite drive forces for pressurization of the fluidstreams passing therethrough. The hydraulic oil then cycles back to thehydraulic pump. In this way, a closed hydraulic system is provided inconnection with the disclosed intensification pump.

With specific reference to FIG. 4A, an exemplary implementation of thepresent disclosure includes a single main hydraulic pump that is adaptedto pump hydraulic fluid, e.g., hydraulic oil, to an hydraulic oilcontrol device. The control device is adapted to control the outflow ofmultiple hydraulic streams, e.g., hydraulic stream 1 and hydraulicstream 2. The control device may be manually controlled and/or subjectto an automatic control system (e.g., a feedback control loop), wherebythe relative levels of outflow may be controlled adjusted. Thus, forexample, outflow to hydraulic stream 1 and outflow to hydraulic stream 2may differ, such that intensifier pump 1 is hydraulically powered to adiffering degree as compared to intensifier pump 2. In this way, theflow of processed streams 1 and 2 may be controlled/metered, therebyallowing variable flow rates to be delivered to the reaction chamber.

With reference to FIG. 4B, an alternative hydraulic system is depictedwherein the main hydraulic pump feeds hydraulic fluid/oil to amanifold/tee which generates hydraulic stream 1 and hydraulic stream 2which, in turn, drive intensifier pumps 1 and 2. As shown in FIG. 4B,the exit flow from intensifier pump 2 is directed to a flow splittingmodule that is adapted to recycle a portion of the reactant stream. Inthis way, the overall flow of reactant 1 and reactant 2 to the reactionchamber may be controlled/metered. Of note, the recycled reactant 2 isat a high pressure, and appropriate check valve arrangements aregenerally included to ensure proper flow of reactant 2 through thedisclosed system. Thus, the flow implementation of FIG. 4B is effectiveto deliver reactants 1 and 2 to the reaction chamber at differing rates,and the control thereof may be effected through variations at the flowsplitting module.

Of note, various alternative system designs may be employed according tothe present disclosure to control the ratio of feed streams delivered tothe microreactor. Thus, in a first alternative system design, upstreammetering of process streams may be employed, e.g., through valve(s),manifold(s) or the like. Each individually metered feed stream is fed tothe intensifier pump(s), either directly (and individually) or as acombined stream (e.g., after combination in a manifold).

In a second alternative system design, feed streams may be fed tointensifier pumps that are arranged in parallel. Each intensifier pumpis associated with its own downstream load, e.g., through recycling of aportion of the high pressure flow exiting the intensifier pump. Meteringof the feed streams may thus be achieved by regulating/controlling thedegree to which each individual stream is recycled after exiting itsassociated intensifier pump. By recycling a greater percentage from aparticular intensifier pump, the relative percentage of such feed streamis reduced from a downstream perspective.

In a further alternative design, the flow of feed streams throughrespective intensifier pumps is controlled/regulated by controlling theflow rate of hydraulic fluid to individual intensifier pumps. Thecontrol of hydraulic fluid flow may be effectuated through appropriatevalving. To the extent a first intensifier pump receives higher levelsof hydraulic fluid relative to a second intensifier pump, the feedstream that is directed to the first intensifier pump will be delivereddownstream at a higher relative level as compared to a feed streamdirected to the second intensifier pump. Indeed, by regulating the flowof hydraulic fluid to an intensifier pump, a piston's rate of travel maybe controlled, thereby directly impacting the fluid flow therethrough.

Each of the disclosed system designs may be advantageously employedaccording to the present disclosure to achieve variable/desiredinteraction ratios between feed streams within the downstreammicroreactor.

B. Exemplary Process Implementations

The disclosed apparatus/system may be used in a wide range ofapplications and/or implementations, e.g., particle size reductionapplications (e.g., emulsion and suspension applications), celldisruption application (e.g., e-coli and yeast applications), andreaction applications (e.g., crystallization applications). Severalexemplary applications/implementations are described herein below.However, such exemplary applications/implementations are merelyillustrative, and are not limiting with respect to the scope of thepresent disclosure.

Before describing specific exemplary implementations of the presentdisclosure by way of “examples” herein below, several broad principleshaving applicability to the disclosed apparatus/systems and theirapplication are described. These broad principles may be employed toidentify, evaluate, implement and/or enhance operations according to thepresent disclosure.

(a) Physical Processes

Examples of physical processes that may be facilitated and/or supportedaccording to the present disclosure include crystallization processes,precipitation processes, emulsion formation processes, particle coatingprocesses and particle mixing processes. The foregoing processesgenerally benefit from molecular interaction at the nanometer scale.Each of these processes can be undertaken using the disclosedapparatus/systems according to different methods and/or roadmaps (i.e.,processing of specific constituents under specific process parameters toachieve specific results), as will be readily apparent to personsskilled in the art. For example, processing a solvent and antisolventstream (and optionally a surfactant) with the disclosed apparatus/systemmay lead to crystallization or precipitation of the solute dissolved inthe solvent stream. Similarly, changing the pH of a solution by mixingthe initial solution with a stream that changes the pH of the finalsolution may result in crystallization and/or precipitation of thesolute.

In addition, emulsions may be formed by direct and continuousinteraction of continuous and dispersed phases, e.g., an oil stream withan aqueous/water stream. Typically, stable emulsions and nano-emulsionsare formed in two steps. Initially, a coarse pre-emulsion is made bymixing the immiscible liquids with conventional mixing equipment, suchas a propeller or a rotor/stator mixer. Subsequently, the coarseemulsion may be processed using a standard MICROFLUIDIZER® processor(Microfluidics Corp., Newton, Mass.) or a high shear homogenizer.However, with the disclosed apparatus/system, the step of producingpre-emulsions may be advantageously avoided.

Further, coating of solid particles can be achieved according to thepresent disclosure by interacting liquid suspensions of solid particleswith a solution containing the desired coating material(s). Coatings canthus be formed by physical or chemical adsorption of the coatingmaterial onto the particle surface.

(b) Chemical Processes (Chemical Reactions)

Chemical reactions of single or multiphase liquids can be enabled and/orexpedited according to the present disclosure, e.g., when reactantstreams are forced to interact inside the fixed, small volume geometryof an interaction chamber/microreactor. Flow through the interactionchamber/microreactor advantageously increases the interaction surfacearea among the reactant streams to a significant degree, therebyminimizing potential diffusion limitations and increasing reactionrates. Undesirable side reactions and/or slow reactions can be minimizedby creating conditions within the disclosed interactionchamber/microreactor, wherein the conditions are analogous to a “wellstirred reactor”. Indeed, the disclosed apparatus/systems may beeffective in avoiding reactions that are a result of concentrationgradients.

Exemplary chemical reaction categories that are supported by thedisclosed apparatus/systems include acid-base reactions, ion exchangeprocesses, reduction/oxidation reactions, polymerization reactions,precipitation reactions, crosslinking reactions, reactivecrystallization reactions, biodiesel reactions, and the like. Moreparticularly, the following exemplary application/implementationcategories may benefit from processing with the disclosedapparatus/system: (i) production of nanoparticles via crystallization,precipitation or chemical reactions; (ii) coating of particles; (iii)mixing of heterogeneous materials at the nanometer scale; (iv)expediting chemical reactions, and (v) Process Intensification

C. Performance Enhancement

According to testing performed according to the present disclosure,mixing intensity may be identified from estimates of the length scalesassociated with turbulent eddies (and thus Kolmogorov diffusion lengths)in the nanometer range. Time scales for the macro-, meso-, andmicro-mixing processes may thus be estimated and, along with the lengthscales, prediction of operational roadmaps may be undertaken thatcorrelate well with transport rates, particle size observations, andwell established theoretical approaches. Such testing permitsenhancement of system performance, such that the disclosed apparatus,systems and methods may be effectively and advantageously used, interalia, to measure millisecond kinetics, conduct micro-scale reactions,facilitate formation of nano-emulsions/suspensions via turbulent mixing,and achieve enhanced mass transfer operations needed for controllednucleation and growth in precipitation and crystallization, e.g., forprotein and inorganic substances.

Representative values for system parameters according to exemplaryimplementations and/or applications of the present disclosure are asfollows:

-   -   reaction chamber residence times from 0.5-1 ms;    -   micro-mixing time scales of 1-4 μs;    -   turbulent energy dissipation rates on the order 10⁷-10⁸ W/kg;    -   nano-emulsion droplet and particle diameters in the range 25-500        nm;    -   diffusion coefficients from 1-5×10⁻⁹ m²/s; and    -   interface transfer coefficients as high as 0.5 m/s.        Chemical conversion and pathway selectivity of 100% can be        advantageously demonstrated according to exemplary        implementations of the present disclosure.

As a general principle, process intensification (PI) facilitatesintegration of operational steps within a smaller number ofscale-reduction vessels, thereby supporting miniaturization of unitoperations and processes. In situ separation schemes within continuousflow micro-reactors are classic examples. Adaptation of PI strategiesbased on the present disclosure provides numerous benefits. Exemplaryadvantageous outcomes that may be realized through adaptation of thedisclosed PI strategies include:

-   -   High throughput with higher product purity and uniformity    -   Efficient start-up and shut-down procedures, which translates        to, inter alia, reduced inventory/surge systems and reduced        “off-specification” material    -   Decreased expenditures, which translates to, inter alia,        low/reduced capital costs, lower energy use and reductions in        other operating costs, and reduced space requirements/smaller        plant footprint    -   Enhanced operability and control    -   Environmental advantages and/or pollution prevention    -   Lower plant profile    -   Safety benefits, which translate to, inter alia, decreased        volumes of explosive, hazardous or toxic compounds, enhanced        operator friendliness, and potential isolation in secondary        containment chambers, as desired

The systems and methods of the present disclosure facilitate improvedreactor performance. In particular, the disclosed reactors can provide anumber of key advantages by, for example, cutting residence times,accelerating reaction rate, minimizing side reactions and/or reducingenergy intensive downstream processing steps, such as distillation andextraction. With many reactions, there are significant heat and masstransfer limitations which are determined by the contacting patternsobtained via the intensity of mixing (i.e., the hydrodynamics). Theseheat/mass transfer limitations can thus control the observed systemdynamics, rather than fundamental kinetics of the reaction system.

Depending on reaction dynamics of a particular system, there are severalways that apparent reaction rate of a particular system can be increasedaccording to the present disclosure. For example, mass transferlimitations that are common to heterogeneous reactions may be removed byincreasing the surface area-to-volume ratio of the dispersed phase. Oncethe mass transfer limitations are removed (or substantially reduced),the reaction may advantageously proceed according to the intrinsickinetics.

As a further example, enhanced identification and/or control of thetemperature profile throughout the reactor may be achieved, whichgenerally leads to better control of the reaction rate. By way ofillustration, a highly exothermic reaction carried out in a large batchvessel may require several hours, not because of any inherent kineticsconstraint but because of the time necessary to remove the heat ofreaction safely via its poor transfer area-to-volume ratio using atraditional coil configuration. With intense mixing and improved heattransfer mechanisms associated with the low holdup of material in thereactor, better productivity is possible according to the presentdisclosure. As a result of these enhanced transportcapabilities/features, the selectivity of a multiple reaction schemeincreases, resulting in improved product yields and quality with reducedseparation requirements.

Of note, process data, coupled with computational fluid dynamics (CFD)modeling, may advantageously provide a basis for design, redesign and/orreconfiguration of system designs and layouts. CFD can also be used topredict: (1) velocity and stress distribution maps in complex reactorperformance studies; (2) transport properties for non-ideal interfaces;and (3) materials processing capabilities useful in encapsulationtechnology and designing functional surfaces, especially whereself-assembly mechanisms, surface tension and interfacial forces, andturbulent energy driven processes dominate.

D. Precipitation and Crystallization Processes

Both precipitation and crystallization processes are characterized by asolid material that is formed from solution. Such processing schemes arewidely used in production of pharmaceutically active ingredients,proteins and other chemical products. The main difference in these twoprocesses is that precipitation produces a solid of poorly definedmorphology, whereas crystals grow with a well defined 3-dimensionallattice structure. Typically, the primary objectives for bothprecipitation and crystallization processes are to (1) increaseconcentration, e.g., when precipitating from a dilute solution, and/or(2) purify a material, such as when selectively crystallizing onespecies from a solution containing multiple types.

Each process is generally initiated by changes in the thermodynamicstate of the solution, thereby reducing the solubility of the targetspecies. Initiation may thus be undertaken via temperatureadjustment(s), concentration adjustment(s), e.g., by addition ofantisolvents, or adjustment of solution activity coefficients, e.g., byaddition of ionic species. As an example, when dealing with solubilityof proteins, processing approaches may include: (1) pH adjustment to theisoelectric point, (2) addition of organic solvents, (3) increasingionic strength to cause salting out, and/or (4) addition of non-ionicpolymers.

Nucleation sites must be created to initiate precipitation and/orcrystallization processes, either by generating a very highsuper-saturation resulting in spontaneous growth (homogeneousnucleation) or seeding the solution with surfaces for growth(heterogeneous nucleation), whether inert or the desired target species.In all cases, it is essential that the solubility of the target speciesbe reduced below the actual concentration in solution. This effectivelycreates a concentration in excess of the thermodynamic equilibriumsaturation value and rate processes then dominate system behavior. Themagnitude of the difference from equilibrium, i.e., degree ofsuper-saturation, influences both type and rate of system response.

Precipitation conditions are often obtained via chemical reactionsproducing species with limited solubility in the reaction mixture. Thisis one method of generating the local high degrees of super-saturationrequired for desired rapid kinetics. The process occurs in four serial,but often overlapping, steps:

-   -   (1) The feed solution and reagent are mixed. The time required        to achieve homogeneity is generally dependent on diffusivity of        the target species and distance the target species molecules        must travel within the mixing eddies (i.e., Kolmogorov length),        which can be estimated using turbulence theory.        Calculation/analysis requires knowledge of the mixing power        input and subsequent energy dissipation rate per unit volume        along with solution properties such as density and viscosity.    -   (2) Subsequent to the mixing step which is aimed at obtaining a        desired degree of super-saturation, nucleation of small solid        particles occurs. The nucleation rate increases exponentially        with respect to super-saturation up to a characteristic limiting        rate, and the features of the product formed depend        significantly on this rate. If the nucleation rate is too high,        the result is likely to be a colloid (i.e., highly solvated)        and, thus, complicated downstream processing may be required.    -   (3) Growth rate is determined by diffusion of solute molecules        from the bulk solution to the solid surface and/or a surface        integration rate, until a limiting particle size is reached. The        limiting particle size is generally determined by the magnitude        of shear in the mixed solution.    -   (4) Once the limiting particle size is reached, further growth        is by flocculation, whereby particles collide and adhere to each        other. Particle number thus decreases with time exponentially as        the particle size increases. Finally, as the particles grow in        size, the shear forces in the mixed solution cause fracture;        resulting in a size plateau at long mixing times.        Thus, important parameters in a precipitation process are (a)        degree of super-saturation achieved in the initial mixing, which        is dependent upon reagent volume, and (b) shear stress in the        mixed solution, which is proportional to power input per unit        volume of solution.

Like precipitation, the crystallization process begins by reducing thesolubility of the target species. However, relatively low degrees ofsuper-saturation are utilized since, at high levels, the solids formedtend to be an amorphous precipitate (rather than crystalline). Controlof the rate processes, as discussed above, is essential to directing thepath to a desired final thermodynamic state and to achieving a desiredmorphology. Spontaneous formation of solids can entrap undesired speciesinto the lattice framework. Thus, slowing the growth rate byreducing/lowering the super-saturation level permits higher selectivityin the surface integration mechanism, i.e., crystals are formed that arevery pure due to exclusion of other contaminate species. Locally highshear forces can also help maintain appropriate/desirable transportgradients. Crystallization may thus be used as a primary separationmethod and/or as a finishing step to yield product of desired purityaccording to the present disclosure.

E. Nano-Encapsulation

The ability to form nanoscale particles and/or emulsions thatencapsulate active ingredients has applicability in many facets of theengineering biosciences. For example, nano-technologies are having amajor impact on drug delivery, molecular targeting, medical imaging andbiosensor development, as well as on cosmetic and personal careproducts, and nutraceutics. Unfortunately, conventional mixing equipmentin which a high shear, elongated flow field is generated near the tip ofhigh-speed blade(s) only generate emulsions with droplet sizes in therange 500 nm and larger. Such emulsions are stable only if sufficientsurface active agents are present to control agglomeration andre-growth. This approach to emulsion stability requires properdistribution of the surfactant for the appropriate surface coverage ofthe droplets, thereby minimizing Oswalt ripening and subsequentundesired size distribution changes. The higher shear rates achievedaccording to the present disclosure advantageously facilitate generationof stable mean particle sizes in the range 50 to 100 nm andrequisite/desired narrow particle size distributions. The disclosedsystems/techniques may also advantageously dispense with the need forsurfactants for stability, dependent upon the surface characteristics ofthe emulsion components and their intended applications.

F. Creating Nano-Scale Particles/Entities

High shear fields have been developed in the interactionchambers/microreactors of the present disclosure to produce particleswith diameters in the range 50 to 100 nm. Such particles are about thesize of the smallest turbulent eddies generated in such processingunits. For example, jet impingement on a solid surface (e.g. Z-typemicroreactor) or with another jet (e.g., Y-type microreactor) has beenshown to be highly efficient. Systems that incorporate high velocitylinear fluid jets that collide can rapidly reduce the scale ofsegregation between the streams. These jets can be considered as free,submerged, or confined. A free jet stream is not affected by the wallsof a surrounding chamber/vessel nor any surrounding fluid, in contrastto submerged jets where viscous drag forces may be significant. Withconfined impinging jets, the dimensions of the chamber/vessel relativeto jet diameter can play a major role in system performance.

The importance of chamber/vessel dimensions relative to jet diameter isapparent from the micro-mixing time and its relative magnitude comparedto the process characteristic time in such jet-based systems. Tominimize process sensitivity to mixing, it is generally necessary toreduce the mixing time constant (including macro-, meso-, andmicro-mixing) to a fraction of the most significant/relevant processtime constant. Length scales are typically used to classify mixingprocesses, i.e., macro-mixing occurs at vessel dimension scale,meso-mixing is at the turbulent eddy scale, and micro-mixing is on thescale of molecular diffusion in stretching fluid lamellae.

According to apparatus/systems of the present disclosure, high-energydissipation is observed in the disclosed microreactor designs becausethe kinetic energy of each stream is converted into a turbulent likemotion as the result of the collision and redirection of the flow, e.g.,within the very small volume defined by the interactionchamber/microreactor, and the associated shear forces. The size ofvirtual cylindrical volume elements of exemplary microreactors of thepresent disclosure may be quantified using computational fluid dynamics(CFD) techniques and has been calculated to be on the order of seven (7)to ten (10) jet diameters for the radial dimension of the impingementplane. The other cylinder dimension (height) has been shown to beindependent of jet diameter and the design thereof is typically relatedto the inter-penetration length of the two jets. In exemplaryembodiments of the present disclosure, the height dimension iscalculated to be about 10 percent of the inter-nozzle (jet separation)distance.

Interfacial mass transfer area may be used to characterize mixingquality and to quantify associated length scales. Using known transferareas, diffusion lengths, and physico-chemical properties of fluids thatpermit measurement of appropriate rate phenomena to determine transportparameters, it is possible to determine an interfacial transfercoefficient, mass diffusivity, and a system characteristic timeconstant. Coupling these fundamental parameters with system geometricconfigurations, operating variables and measured performance metrics(such as quantity transported and approach to equilibrium, if notobtained), it is possible to determine transfer areas that mustnecessarily be present in an interaction chamber/microreactor. Inaddition, from this interfacial area, it is possible to identify theeddy size scale (i.e., Kolmogorov diffusion length). Consequently, ameasure of mixing intensity can be obtained which provides a basis forpredicting and/or achieving desired average droplet sizes whengenerating nano-emulsions and other dispersed systems.

G. Flow Patterns, Mixing and Transport Phenomena

As is readily apparent, it is important to design systems withappropriate hydrodynamic characteristics with respect to transportphenomena and effects on dynamic response (whether chemical reactionkinetics or other rate processes). Beyond system design, processinnovations are disclosed herein that (i) utilize flow instabilities formixing, (ii) improve contacting patterns to enhance interactions thatpromote better kinetics performance and transport rates, and (iii)improve transport via mechanical turbulence promoters.

EXAMPLES Example 1 Production of Norfloxacin Nanosuspension UsingSolvent/Antisolvent Crystallization at High Shear Rate Conditions

Overview: Hydrophobic active pharmaceutical ingredients (APIs) are oftendifficult to deliver effectively due to formulation limitations.Nanosuspensions of such drugs may be used to increase bioavailabilityand offer a variety of delivery options, including inhalation, oral,transdermal and injection. Apparatus, systems and methods of the presentdisclosure have been used to reproducibly generate sub-micron APIsuspensions via a continuous process that involves solvent-antisolventcrystallization. This technique of generating a supersaturation state,using a miscible fluid to change solvent composition, is readilyimplemented commercially. It may also be the best choice economicallydue to its process intensification character that minimizes unitoperation and energy requirements. Consequently, it may be the mostenvironmentally friendly of the various alternatives. Proof of conceptexperiments were conducted in which nanosuspensions of Norfloxacin(NFN), an antibacterial agent, with median particle sizes in the 170-350nm range and narrow particle size distributions were produced.

In particular, the disclosed apparatus/system facilitates precise mixingof two (or more) reactant streams within a microliter sized interactionchamber/microreactor, where extremely high levels of shear stress andturbulence are induced. The system design provides precise control ofthe feed rates and the subsequent location and intensity of thetransport and reaction processes. With respect to the crystallizationprocess, this ensures control of the nucleation and growth processes,resulting in uniform crystal growth and stabilization rates. The desiredparticle size distribution is thus obtained by precise manipulation ofthe process parameters that established the operational roadmap. Energyinput is manifested as fluid pressure at the outlet of the intensifierpump, and subsequent dissipation mechanisms are determined, at least inpart, by fluid composition, that is its physico-chemicalcharacteristics. Consequently, the energy input establishes mixingintensity and system temperature through viscous heating, energytransfer to the environment, and the formation and surface energiesrelated to nucleation and growth. The other major control variable isdegree of super-saturation as determined by the ratio of solvent andantisolvent streams and system temperature.

Norfloxacin (NFN), which is a highly hydrophobic pharmaceutical, wasselected as a model drug to demonstrate the applicability of thedisclosed apparatus, systems and methods based on: (a) limited watersolubility, (b) availability, and (c) price. The solvent/antisolventsystem selected for this model drug was dimethyl-sulfoxide (DMSO) andwater. The metrics used to evaluate performance are associated withcrystal size, distribution, morphology, and their percent recovery.Light scattering, scanning electron microscopy and x-ray diffractiontechniques were used for both qualitative and quantitative analysis ofthe rod shaped crystals that exhibited very high crystallinity levels.Gravimetric analysis was used for solubility and recoverydeterminations. The main process variables were system pressure (energyinput), feed rates (for solution composition and thus super-saturationratio), and microreactor design/configuration (which determines shearrates and energy dissipation mechanisms)

Experimental Apparatus and Procedure: FIG. 3 provides a schematicdiagram of a system used in this example. A hydraulic pump transportsoil to an intensifier pump that is designed to pressurize the reactantstream(s) to 207 MPa (30,000 psi). Flow through the microreactor ischaracterized by high fluid velocities inside fixed geometrymicrochannels. As a result, high intensity shear fields are generatedand intense energy dissipation mechanisms, such as turbulence areactivated. Under these conditions, mixing of reactants takes place atthe nanometer scale within time scales much shorter than chamberresidence times. Thus, equilibrium conditions are feasibly obtained,where appropriate. Both multi-phase and single-phase reactions arefeasible.

A lab scale, dual feed reaction processor of the type depicted in FIG. 3was used for the experimental runs described in this Example 1. Twoports located upstream of the interaction chamber permitted introductionof two reactant streams into the intensifier pump. The reactants arecoarsely mixed at this point, while the intense mixing advantageouslytakes place further downstream inside the microreactor.

Of note, for systems/implementations where coarse pre-mixing may beproblematic, alternative apparatus/system designs are provided accordingto the present disclosure that enable the reactant streams to mix forthe first time inside the microreactor. These alternative designs arebest suited for applications that include very fast processes withselectivity issues due to the multiple time scales present. To suppressthe slower process that may form undesired by-product(s), the reactantsare first subjected to mixing forces within the interaction chamber. Ineither case, precise control of individual feed streams is important toobtain desired microreactor performance.

The microreactor design is critical to provide/establish a micro-mixingenvironment inside a volume/chamber with dimensions at the micro-literscale. A combination of shear and impact disperse the reactant streamsinto submicron eddies that intermingle and have very highinterfacial/surface area. This promotes rapid development of homogeneousconditions within the micro-liter chamber, since the time scales formicro-mixing (4 μs) and meso-mixing (20 μs) are much smaller than thehydraulic residence time, which is on the order of 1 ms.

The microreactor chamber disclosed herein consists of channels withdepth and width in the range of 75-150 microns, which are several timessmaller than channels in other impinging jet designs. The microreactorchamber design used for the tests of Example 1 includes channels withminimum dimension of 75 microns. Pressures up to 207 MPa (30,000 psi)are required to drive fluids through the channels. With reference to theschematic depiction of FIG. 3, the combined feed stream was splitequally prior to entering the feed channels which feed to theimpingement zone.

The fluids accelerate up to 300 m/s, forming two opposing jets thatimpact one another. As shown in FIG. 2A, the jets collide in a highenergy impact zone with sufficient energy to develop the desireddissipation levels. Nominal shear rates developed within the channelsmay be calculated by assuming a 1-D flow field representation. Thedeformation rate tensor, composed of the various velocity componentspecial derivatives, is thus approximated as the ratio of the averagevelocity inside the channels, u_(avg), and the smallest dimension of thechannel, d_(min). For a Newtonian fluid, this is related to the nominalshear stress (τ) and the dynamic viscosity of the fluid (μ) as:

${\frac{\tau}{\mu}} = \frac{u_{avg}}{d_{\min}}$

The shear rates for the conditions of the present experiments areestimated to range from 5×10⁶ s⁻¹ to 8×10⁶ s⁻¹.

The disclosed apparatus/system is advantageously designed to facilitatecontrol of the major thermodynamic and transport mechanisms of acrystallization process, e.g., the target species solubility,super-saturation ratio and energy allocation/dissipation. This controlis accomplished by manipulation of: (a) the ratio of thesolvent/antisolvent streams, (b) the shear rate and the energydissipation on the reactants, and (c) the temperature history duringprocessing.

Thus, in the experimental tests described herein, the ratio of thereactant streams was controlled by using a metering pump system. Thetotal flow rate of the system depends on the design of the microreactorand the process pressure, which determines shear rate and energydissipation. The temperature history of the fluid is controlled bymaintaining the apparatus/system (e.g., the piping) at the desiredtemperature. Downstream of the microreactor, a heat exchanger is used toreduce fluid temperature, which is elevated during processing as aresult of viscous energy dissipation.

When processing a solvent/antisolvent system, the intense mixing resultsin a homogeneous liquid, i.e., uniform composition down to theKolmogorov scale and, hence, the super-saturation state is similarthroughout the region. Consequently, the resulting crystals areessentially homogeneous in size, degree of crystallinity, and purity,since all crystals form under similar conditions. However, since theprocess is dependent upon the diffusion process within the Kolmogoroveddies to obtain complete uniformity, minor variations at the molecularlevel will still lead to slight differences in nucleation rates. Thus, aparticle size distribution, albeit narrow, is observed.

Solubility Measurements: The solubility of NFN (Sigma-Aldrich, US) inboth water and water-DMSO (Sigma-Aldrich, US) solutions at 20° C. wasdetermined in batch experiments. Water was mixed with a DMSO-NFNsolution of known concentration, while maintaining miscible conditions,to obtain a super-saturation state. The subsequent NFN crystals werepermitted to grow for a period of 10 hours to once again reach anequilibrium state, thereby reaching the solubility limit. The crystalswere filtered from the liquid, then dried in a vacuum oven for about 10hours at 90° C., and weighed. The filtered liquid phase was evaporatedto dryness and the mass of the solid residue determined gravimetrically.The mass balance of the NFN (total amount recovered/amount dissolved)was also determined to establish precision of the solubility limitestimate. The closure was always greater than 90 percent.

The solubility data were used to estimate super-saturation ratios andthe theoretical efficiency of the process, which is defined as thepercentage of the drug present in the solvent that precipitates as thesolvent and antisolvent streams mix.

Crystallization: Crystallization experiments were performed using anexemplary reaction processor of the type depicted in FIG. 3. The solventphase was fed into an intensifier pump using a peristaltic pump. Thewater phase was placed in the inlet reservoir and gravity fed. The twostreams were blended at the inlet to the intensifier pump, noting that alow level of macro-mixing will occur at this process stage.

The total flow rate through the system was controlled by themicroreactor design and process pressure. By varying the flow ratethrough the peristaltic pump at each processing pressure, various mixingratios of the two streams were achieved. The following solvent-to-watervolume ratios were examined: 1:3, 1:4, and 1:10. Equivalently, the waterconcentrations in the final mixture by weight were 73, 78 and 93%,respectively. A total of 250 ml were processed in each experiment.

In addition to super-saturation, the effect of process pressure, NFNconcentration in the solvent stream, and the presence of a surfactantwere investigated. Five operating pressures in the range of 68.9 to 138MPa (10,000 to 20,000 psi) were selected. The concentration of NFN inDMSO varied from 5 to 20 mg NFN/ml DMSO. To determine if a surfaceactive agent could help control particle size, a 1% aqueous solution ofSuluton (BASF) was used to replace water as the anti-solvent, theconcept being that the hydrophobic group of this amphoteric moleculewould interact with the crystal surface at some threshold size, forminga barrier to further transport to and/or along the surface.

To provide appropriate controls for comparison, additional crystalproduction experiments were conducted by mixing the NFN/DMSO solutionwith water in a beaker at very low shear conditions. After mixing toobtain uniformity, NFN was allowed to form crystals under quiescentconditions. Size and shape characterization studies were performed. Thecrystals were then suspended in a saturated solution to conduct particlesize reduction experiments under high shear rates using standardMicrofluidizer® technology. The purpose was to compare this sizereduction process on already grown crystals (“top-down” process) withthe in situ process of growing crystal to the desired size with theapparatus/system of the present disclosure (“bottom-up” process).

Material analysis and characterization: Various techniques were employedto analyze and/or characterize the experimental test results describedherein.

Particle size analysis: The particle size distribution of thenano-suspensions was measured by two different methods:

-   -   (a) Light scattering using a Horiba 910 particle size analyzer:        This instrument has a wide dynamic range of between 20 nm-1000        microns.    -   (b) Dynamic light scattering using a Malvern NanoS particle size        analyzer: This instrument has a dynamic range of 0.5 nm-6        microns

Scanning Electron Microscopy (SEM): A Hitachi S-4800 field-emission SEMwas used to examine the surface structure and shape of the drugparticles and also to verify qualitatively the particle size obtainedfrom the particle size analyzers.

X-ray Diffration (XRD): The samples were analyzed using a Rigaku UltimaIII diffractometer. XRD analysis was used to investigate the effect ofthe processing conditions on the crystalline characteristics, i.e.,structure, percent of crystallinity and crystallite size of NFN.

Results: The following results were achieved herein.

Solubility experiments: TABLE 1 and FIG. 5 summarize the resultsobtained in the solubility experiments. Also included is the maximumtheoretical yield of the drug as a result of solvent/antisolventprecipitation for this system. The closure of the mass balance of NFN(total amount recovered/amount dissolved) in all of the experiments wasgreater than 90%.

TABLE 1 Solubility data of NFN in water/DMSO mixtures at 20° C. WaterConcentration % NFN precipitation (wt % water in NFN solubility fromsaturated solution) (mg drug/g solution) DMSO solution 0.00 21.00 0.009.17 7.18 43.39 28.04 1.57 86.39 47.62 0.86 91.43 57.69 0.64 92.86 73.170.71 89.52 90.19 0.00 100.00It can be seen from the data set forth in TABLE 1 and FIG. 5 that thesolubility of NFN decreases rapidly with addition of water to the DMSOsolution. Dilution to 28 wt % water results in a reduction of NFNsolubility of over 13 times or, equivalently, results in precipitationof over 86% of NFN from its original equilibrium state. As the amount ofwater is increased, the amount of NFN that precipitates also increases.At 50 wt % water, about 92% of NFN precipitates, demonstrating that thedisclosed “bottom-up” process is highly efficient.

Crystallization experiments: FIG. 6 is a representative sample particlesize distribution curve for NFN crystals obtained using the Horibainstrument. This suspension was produced at 138 MPa process pressure, 5mg NFN/ml DMSO, mixing ratio of DMSO to water of 1:4, and passed throughthe disclosed processing system twice. The distribution has a medianparticle size of 186 nm. Most of the material is in the submicron range(peak at 166 nm). A fraction of a percent of the material forms 1 to 10micron agglomerates.

FIG. 7 is an SEM picture of the same NFN crystal material. It can beseen that the particles form needles, 70-100 nm wide and 200-300 nmlong. It can also be seen that the particles have a tendency to formagglomerates by attaching to each other along their length axis duringthe drying process.

FIG. 8 shows the “measured” median particle size (as calculated by theinstrument software) as a function of process pressure. The initialconcentration of NFN was 10 mg/ml of DMSO alone, and the volume ratio ofDMSO to water in the final solution was 1:4 (or equivalently 78 wt. %water). The fluid was passed twice through the disclosed processingsystem. It can be seen that the particle size shows a tendency todecrease with increasing pressure, i.e., from approximately 320 nm at 60MPa to about 200 nm at 140 MPa.

If the system behaves ideally, then theory states that the “solute free”composition of this miscible solvent/anti-solvent system will notinfluence the phenomenological events, other than through its impact onsuper-saturation. That is, concentration can be used as the drivingforce versus activity as related to free energy. As long as the solutionactivity coefficient remains constant over the solute free compositionrange, than the path to the same super-saturation state is irrelevant.To confirm this behavior for the disclosed “bottom-up” system,experiments were conducted in which identical super-saturation ratioswere obtained by (i) varying the initial concentration of NFN in DMSOalone and keeping the DMSO/water ratio fixed at 1:4, and (ii) varyingthe DMSO/water ratio (1:3, 1:4, 1:10) along with the initial NFNconcentration, as needed. The results presented in FIGS. 9 and 10 (cases(i) and (ii), respectively) confirm that only the super-saturation rationeed be considered over the range of solute free fluid compositionsstudied.

FIG. 9 shows the median particle size as a function of NFN concentrationin DMSO. The process pressure was 138 MPa and the volume ratio of DMSOto water was 1:4 (or equivalently 78 wt. % water in the final solution).The fluid was passed twice through the disclosed processing system. Itcan be seen that the particle size increases from a minimum ofapproximately 190 nm at a concentration of 5 mg NFN/g DMSO to nearly 340nm at a concentration of 20 mg NFN/g DMSO. It is noted that thesolubility limit of NFN in DMSO is about 21 mg NFN/g DMSO at ambienttemperature.

FIG. 10 shows the effect of supersaturation ratio on the particle sizewhen the process pressure is held at 138 MPa (as obtained using bothmethods). It can be seen that the particle size decreases as thesupersaturation ratio decreases over the range of process parametersstudied in these experiments. Initially, this result seems inconsistentwith the concept that high super-saturation yields small crystals due tothe large number of nuclei formed under these conditions. However, thehigh shear rates and resultant micro-mixing conditions essentiallyeliminate the mass transfer controlled kinetics mechanism for growth,thereby establishing interfacial attachment kinetics as the controllingmechanism. The rate of growth is thus higher for higher super-saturationconditions (more cluster attachment). Since the scale for the mixingevents are identical in these experiments as reported in FIGS. 9 and 10,the plateau particle size, albeit still at the nanoscale, is larger.

The effect of supersaturation ratio on the theoretical efficiency of theprocess at 138 MPa is shown in FIG. 11. The theoretical efficiencycorresponds to the percentage of NFN that precipitates as a result ofsolubility change. In the present examples, the theoretical efficiencyincreases from 32% at a supersaturation ratio of about 1.5 to 85% at aratio of about 7.

The anticipated role of a surfactant was not realized in the disclosedsystems, as is shown in FIG. 12. The particle size distribution with andwithout introduction of Suluton surfactant is similar. In particular,the median particle size varied from 204 nm to 209 nm, respectively. Themain peak of the distribution is in the same location in both cases.However, there is a secondary population of agglomerates in the samplewithout surfactant with sizes 1-10 microns. This population of particlesis significantly smaller in the sample that contains surfactant.

Particle Size Reduction with High Shear Processing: To provide a basisfor validation, standard particle reduction experiments (i.e.,“top-down” processing) were performed. Crystallization of the NFN in alow shear environment produced long, narrow particles (see FIG. 13A).The particles were up to 1 mm long and were 1 to 3 microns wide. Afterthe particles were grown, the dispersion was processed in a standardMicrofluidizer® unit equipped with a high shear interaction chamber.Applying these high shear conditions for 30 passes using an H30Z (200microns)-G10Z (87 microns) chamber configuration at 207 MPa, thecrystals were reduced to a median particle size of 428 nm (see FIG.13B). This is essentially twice the median particle size of crystalsproduced using the advantageous apparatus, systems and methods of thepresent disclosure (“bottom-up” processing), which required only twopasses through the system.

XRD Analysis: The XRD spectra of NFN crystal samples that were producedfrom the DMSO/water system under all processing conditions showed nostatistically significant differences. These samples included NFNnanoparticles that were produced using the apparatus, systems andmethods of the present disclosure, as well as NFN needles that wereprepared at low shear and at no shear at all. The XRD spectra are shownin FIG. 14. NFN as purchased shows a different XRD pattern, as seen inFIG. 15.

The percent crystallinity and average crystallite sizes are given inTABLE 2. The results indicate that the shear rates duringcrystallization affect both the percent of crystallinity and thecrystallite size, and that each are highest at no shear. The percent ofcrystallinity decreases slightly from 85% to 78% as shear is appliedduring crystallization. The crystallite size changes dramatically from727 Å at no shear to 239 Å at high shear conditions.

TABLE 2 Percent of crystallinity and average crystallite sizes asmeasured by XRD Percent Crystallinity Average Crystallite Sample (±4%)Size (Å) As purchased 84.1 441 Re-crystallized (no shear) 85.1 727Re-crystallized (low shear) 77.8 275 Re-crystallized (high shear) 79.7239

Discussion: Segregation of the solvent and antisolvent streams untilimmediately before the high shear mixing zone was critical in producingNFN nanosuspensions. It is reasonable to assume that the bulk of nucleiform after intense mixing takes place within the microreactor of thedisclosed apparatus/system. Some nuclei may also form inside theintensifier pump prior to the microreactor chamber. However, mixinginside the microreactor is at the nanometer scale, while the limitedmixing that occurs inside the intensifier pump is at a scale that isorders of magnitude larger. Therefore, the nucleation rate should bemuch higher inside the microreactor than in any other location in thesystem—where mixing is not at that scale.

Crystal growth takes place after nucleation. As noted above, incrystallization processes, a large concentration of nuclei formed underhigh super-saturation conditions usually results in small sizeparticles. Also in crystallization processes, high shear limits crystalgrowth due to “mechanical” forces exceeding cohesive and interfacialforces. In this case, the combination of large concentration of nucleiand high shear yield NFN nanoparticles.

Originally, the purpose of using a surfactant was to coat the particlesso crystal growth slowed down. However, the surfactant that was used didnot have any effect on primary particle size in the present experiments.It is possible that the solubility of the surfactant in the DMSO/watermixture was high enough so that the surfactant remained in solutioninstead of coating the particles and/or that highly stable micellesformed once the solubility limit was exceeded (i.e., critical micelleconcentration). Surface tension and interfacial energy associated withthese self-assembly processes play a significant role. Anotherpossibility is that the crystal growth was faster than the coatingprocess and an activation energy difference/barrier also contributed.

The crystalline structure of NFN did not vary with the shear rate thatwas applied to the fluid or with the supersaturation ratio. However, thecrystalline structure of NFN crystals produced according to the presentdisclosure did differ from the crystalline structure of NFN, aspurchased. It is possible that the crystalline structure of NFN producedby the disclosed apparatus/system and method is related to thesolvent/antisolvent fluid system used for crystallization. The percentcrystallinity did not appear to be a strong function of shear rates. Incontrast, the crystallite size is significantly reduced with an increasein shear rates.

Summary: The disclosed apparatus, system and method can be used toeffectively produce nanosuspensions from a broad range of activepharmaceutical ingredients (APIs). The choice of solvent and antisolventsystem is critical, since it will control the solubility of the API,hence supersaturation, which is the driving force of crystallization.There may be systems in which the crystallization process is fast, suchthat the API crystallizes before entering the microreactor. However,alternative embodiments of the disclosed apparatus/system—which aredesigned to keep the two reactant streams separate prior to entering themicroliter volume of the microreactor—may be advantageously employed insuch circumstances.

More particularly and as demonstrated by the experimental resultsreported herein, the disclosed apparatus, system and method weresuccessful in producing NFN nanosuspensions using a continuoussolvent/antisolvent crystallization process. The disclosed technologyprovides intense mixing of the streams in a microliter size volume,ensuring that a micro-mixing scale is advantageously reached. Inaddition, limited mixing of the two reactant streams occurred prior toentering the microliter microreactor. Consequently, only Kolmogorovlength scale diffusion determines system performance and nanometerparticles are formed.

The solvent/antisolvent system included two miscible fluids, DMSO as thesolvent and water as the antisolvent. The formed particles were needleshaped, 70 to 100 nm wide and 200 to 300 nm long. The median particlesize, as measured by laser scattering, varied in the range of 180 to 400nm.

The effect of process pressure (determining energy input), the NFNconcentration, the supersaturation ratio and the presence of surfactanton the particle size and the crystallized material were investigated.Higher pressures resulted in smaller particle sizes, as did lowering NFNconcentration and supersaturation ratios. The surfactant that was used(Solutol) did not affect the particle size. The crystalline structure ofthe material formed in the DMSO/water system was not affected by theshear rate of the process. However, the crystallite size of the materialdecreased threefold when comparing no-shear crystallization to highshear crystallization.

The theoretical efficiency of crystallization, as calculated based onthe solubilities of NFN in DMSO/water, varied in the range 38 to 83%,dependent upon the increasing magnitude of the supersaturation ratio.Lower values of this ratio resulted in smaller particles, but at theexpense of lower rates and efficiencies.

Example 2 Production of Stable Drug Nanosuspensions According to thePresent Disclosure (Extension of Example 1)

Several active pharmaceutical ingredients (APIs) were tested to furtherdemonstrate the efficacy of the disclosed apparatus, systems andmethods. The median particle sizes of suspensions produced by theapparatus/systems of the present disclosure varied in the range of50-767 nm. The suspensions were stable with a single exception. Forcertain APIs, the process efficiency exceeded 80%.

As opposed to conventional “top-down” methods for manufacturingnanosuspensions, which primarily rely on reducing particle size of drugpowders in dry or wet formulations, exemplary embodiments of the presentdisclosure employ “bottom-up” processing using solvent and antisolventcrystallization to produce drug nanosuspensions. The disclosed“bottom-up” processes allow the formation and stabilization ofnanosuspensions without the need for size reduction. More particularly,the disclosed apparatus/system and associated “bottom-up” processingprovide precise control of feed rate and mixing location of reactants,thereby ensuring control of nucleation and growth processes andresulting in uniform crystal growth and stabilization rates.

Determination of Solubilities: The approximate solubilities of the APIsin the solvent and various solvent/antisolvent solutions weredetermined, whenever possible. It was not possible to obtain solubilitydata for all APIs and/or at all conditions of interest, primarily due toinadequate quantities of such APIs. In such cases, simple tests wereconducted by mixing solutions of APIs with the antisolvent to ensureadequate precipitation, as described below.

Crystallization Experiments: Crystallization experiments using thedisclosed apparatus/system were conducted at 138 and 83 MPa (20,000 and12,000 psi) process pressures. The reaction chamber that was used had aminimum channel dimension of 75 microns. The solvents were eitherdimethyl sulfoxide (DMSO) or N-Methyl-2-Pyrrolidone (NMP), and theantisolvent was water (see TABLE 3). Of note, alternative solventsinclude methanol, ethanol, acetone, dichloromethane, octanol andisopropyl alcohol, and alternative antisolvents include hexane andheptane. The water volume flow rate was typically 3-10 times the solventvolume flow rate, resulting in supersaturation between 1.4 and 9.

Whenever the solubilities were known, the solvent to antisolvent ratiowas determined by the supersaturation. When the solubilities were notknown, a test was conducted which involved adding water to an APIsolution to determine conditions under which a substantial amount of theAPI had crystallized and precipitated. This condition was then modified(as seen fit) based on the results of the crystallization experiments.

A surfactant was added to the antisolvent (water) in order to: (a)stabilize the nanoparticles and limit their growth, and (b) minimizeagglomeration of the particles and to thereby create a stablesuspension. Two non-ionic surfactants were used, Solutol® HS 15(polyoxyethylene esters of 12-hydroxystearic acid; Bayer) and ahydrophobically modified insulin polymeric surfactant, INUTEK SP1(Orafti).

TABLE 3 Anti- Ratio Process Solvent solvent (AS)/(Sol) API conc. Surfac-Pressure API Function (Sol) (AS) (mg/ml) in solvent tant (MPa)Azithromycin Antibiotic DMSO Water 4 75 Solutol 138 Oxycarbazepine Anti-DMSO Water 4 40 Solutol 138 convulsant API-1 NSAIS NMP Water 5 50Solutol/ 83 None API-2 Antibiotic DMSO Water 3-10 5-20 Solutol/ 138 NoneLoratadine Anti- NMP/ Water 4 & 10 40 & 100 Solutol/ 138 histamine DMSOINUTEK

The disclosed “bottom up” process for producing nanosuspensions wascompared to a typical “top down” process. As a typical “top down”process, the standard Microfluidizer® technology was selected. Thistechnology is routinely used for particle size reduction of dispersionsand emulsions in a variety of industries, including the pharmaceuticalindustry.

For the “top down” control experiments, suspensions of micron sizecrystals were processed with a conventional Microfluidizer® high shearprocessor. These crystals had been grown under no shear conditions bypouring the solvent and antisolvent streams into a beaker and thenallowing the crystals to grow without stirring the fluids.

Five different model APIs were used for testing, as listed in TABLE 3.The APIs were selected from different chemical families and exhibiteddifferent pharmacological activities. In particular, there were twoantibiotics (azithromycin and API-2), an antihistamine (loratadine), ananticonvulsant (oxycarbazepine) and a non-steroidal anti-inflammatory(NSAIS, API-1). The molecular weights of the APIs were in the range of228-749.

Material Characterization: Material characterization was performed inthe same manner as described above with reference to Example 1.

Results: TABLE 4 sets forth the results from crystallization experimentsfor the noted APIs. Particle size and shape, the measuring/visualizationmethods and details of the crystallization process are also set forth inTABLE 4.

TABLE 4 Median Particle Size Measurement Surfactant Processing API (nm)Method Shape Stability (Solvent) Method Azithromycin  50-100 TEM/DLSSpheroidal Stable Solutol Disclosed System Oxycarbazepine 767 SLSUnknown Stable Solutol Disclosed System Oxycarbazepine   5000 × 20,000SLS Needle Stable Solutol Control Oxycarbazepine 1200 SLS Stable SolutolControl with size reduction after 25 passes API-1 397 SLS Unknown StableSolutol/None Disclosed System API-2 166-312 SEM/LS Needle StableSolutol/None Disclosed System Loratadine 183 DLS Unknown Very SolutolDisclosed unstable (NMP) System Loratadine 379 DLS Needle Rather INUTEK(NMP) Disclosed unstable System Loratadine 90 DLS Unknown Very SolutolDisclosed unstable (DMSO) System Loratadine 332 DLS Needle Rather INUTEKDisclosed unstable (DMSO) System

As shown in TABLE 4, crystallization of azithromycin using the disclosedapparatus/system resulted in a nanosuspension with median particle sizeof 50-100 nm. The particle size was measured using DLS and was confirmedby TEM (see FIG. 16). The nanosuspension was stable both in the solventand antisolvent mixture, and in water after the solvent was removed.

As also shown in TABLE 4, crystallization of oxycarbazepine using thedisclosed apparatus/system resulted in stable nanosuspensions withmedian particle size of 767 nm, as determined by SLS. The particle sizedistribution was bimodal, with a peak at about 340 nm and another atabout 1 micron. It is possible that the smaller particle population is aresult of crystallization taking place inside the reaction chamber. Thelarger particle population may be a result of crystallization startingprior to the interaction chamber. Finally, about 5% of the particles byvolume were in the range of 2.5-6 microns.

In contrast, crystallization of oxycarbazepine under control conditions(beaker) resulted in needles having lengths of about 20 microns andwidths of about 5 microns. The particle size of the controloxycarbazepine sample was reduced using a standard Microfluidizer®processor (“top-down” process). The median particle size of the samplewas reduced to 1.2 microns after 25 passes through the processor. Theprocessed sample contained a population of about 5% of particles withsizes in the range of 4-6 microns. Therefore, smaller particles wereadvantageously produced using the apparatus/system of the presentdisclosure in a single step as compared to conventional “top-down”processing that included reducing the particle size in multiple (25)steps.

With further reference to TABLE 4, crystallization of API-1 using theapparatus/system of the present disclosure resulted in stablenanosuspensions with median particle size of 400 nm, as determined bySLS. The presence of surfactant, Solutol, did not affect the primaryparticle size of the suspension, but it reduced the propensity of theparticles to agglomerate.

Crystallization of API-2 using the apparatus/system of the presentdisclosure resulted in stable nanosuspensions with median particle sizesof 166-312 nm, as determined by SEM and SLS. Similarly to API-1, thepresence of surfactant (Solutol) did not affect the primary particlesize of the API-2 suspension. The median particle size of API-2 and theprocess efficiency decreased as supersaturation decreased from about 8to 1.4. The efficiency varied in the range of 32% and 83%.

Loratadine exhibited very different behavior than all other APIs testedherein. Submicron particles were formed immediately after using theapparatus/system of the present disclosure or mixing the solvent andantisolvent streams in a beaker. However, the suspension was unstablesince the particles grew, sometimes during particle size measurements.

Different surfactants and solvents were investigated in an effort toincrease the stability of the loratadine suspension. When Solutol wasused as a surfactant, the initial particle size was about 90 nm, but areproducible particle size measurement was difficult or impossible toachieve. This was true with both solvents that were tried, DMSO and NMP.When INUTEK was used as a surfactant, the resulting particle size waslarger, on the order of 332-379 nm. However, the stability of theparticles was much higher.

Overnight, the loratadine particles that were produced with theapparatus/system of the present disclosure formed uniform needles thatwere 10-20 microns long and 0.5-2 microns wide. The particles that wereproduced with the control method formed needles of hundreds of micronsin length and tens of microns in width.

Summary: The apparatus, system and method of the present disclosureprovides a continuous and scalable microreactor technology. Highpressures force liquid reactants to form jets with velocities up to 400m/s. The jets experience/encounter high shear fields in a microliterscale volume, forcing the reactants to mix at the nanometer scale,minimizing diffusion limitations.

The disclosed apparatus/system was successfully used to producenanosuspensions of model APIs using solvent/antisolvent crystallization.The median particle size varied in the range of 50-767 nm. Thesuspensions were stable after production, with a single exception. Thestability of the less stable suspension could be influenced bysurfactant selection. In addition, the disclosed “bottom-up” processingmethod was demonstrated to be more effective in producingnanosuspensions than standard, particle size reducing (“top-down”)methods.

Example 4 Proposed System Dynamics for Biodiesel Synthesis

Biodiesel may be produced by the transesterification of vegetable oil.The most common vegetable oils used are soybean oil and rapeseed oil.The reaction is a three-step catalytic, reversible reaction. For eachmole of the triglyceride (TG) reactant (i.e., three fatty acid sidegroups), three moles of methanol are required to produce three moles ofthe specific fatty acid methyl esters (FAME, identified as “biodiesel”),and one mole of glycerol (G, the byproduct). However, the reaction iscarried out in an excess of methanol (6:1 molar ratio methanol tovegetable oil) in order to drive the reaction in the forward direction.The primary reaction scheme is shown in FIG. 20.

Typically, the catalyst is sodium hydroxide or sodium methoxide. Ineither case, the ion responsible for the catalytic action is themethoxide ion. When sodium hydroxide is used, the methoxide ion isgenerated in situ by reaction with methanol. The reaction mechanism foralkali-catalyzed transesterification was formulated as three steps (Ma,F., Hanna, M. A., “Biodiesel production: a review”, BioresourceTechnology, 70, 1-5, (1999)). The key step is the formation of anactivated complex between the TG molecule and the methoxide ioncatalyst, thereby promoting selective conversion of TG versus the freefatty acids (FFA). The much slower, non-catalytic reaction involving FFAforms undesired side products (“soaps”) that act as surface activeagents stabilizing any emulsion formed and thus generating downstreamprocessing problems.

Since an important factor in accelerating the desired reaction is thedegree of mixing between the alcohol and triglyceride phases, which areimmiscible, the formation of a large interfacial area is sought.Unfortunately, this can also be problematic if the side reaction is notsufficiently suppressed. An environment that eliminates transportresistances and thus permits the process to progress at its intrinsickinetics rates can overcome this problem. Since the desired rate willnow be much greater than the undesired, the reactants are consumedbefore they can follow the other pathways within this reaction networkand/or the system can be quenched in some manner once sufficientconversion of desired product is obtained. Furthermore, the need forthis large transfer area is required for only an initial lag period.

Accordingly, the important reaction events should proceed as follows.First, the catalyst dissolves in the methanol phase and hence thereaction is limited by the oil concentration in that phase (Vicente G.,Martinez, M., Aracil, J., Esteban, A., “Kinetics of sunflower oilmethanolysis”, Industrial and Engineering Chemistry Research, 44,5447-5454, (2005)). Thus, there is an initial mass transfer limitedregion in which efficient contact of the two phases has to be achieved.In this stage, the reaction occurs at the interface (Boocock, D. G. B.,Konar, S. K., Mao, V., Sadi H., “Fast one-phase oil-rich processes forthe preparation of vegetable oil methyl esters”, Biomass and Bioenergy,1, 43-50, (1996)). The glycerol that is formed diffuses into themethanol phase and the FAME diffuses into the oil phase. As the massfraction of FAME increases, the solubility of methanol in the FAME+oilphase increases (Zhou H., Lu H., Liang B., “Solubility of multicomponentsystems in the biodiesel production by transesterification of Jatrophacucras L. oil with methanol”, Journal of Chemical Engineering Data, 51,1130-1135, (2006)). The ternary mixture of FAME+oil+methanol becomes ahomogeneous solution when the mass fraction of FAME increases to around60-70%. The reaction now takes place in this homogeneous phase.

It should be noted however that the reaction mixture is stillheterogeneous. Since the solubility of glycerol in FAME and methanol islow (Zhou et al., 2006), the glycerol remains as a separate phase andthe methanol partitions between the glycerol and FAME phases. In orderto model the kinetics of the reaction in the homogeneous phase, it isnecessary to have data on how the methanol partitions between the FAMEand glycerol phases. Note also that if significant surfactants have beengenerated, the separation of these two immiscible product phases is nowdifficult, requiring emulsion breaking techniques and associatedvessels.

Kinetics of the biodiesel reaction: Rate constants have been reportedfor the transesterification of soybean oil with methanol at a catalyst(NaOH) concentration of 0.2% and a temperature of 50° C. (Noreddini, H.,Zhou, D., “Kinetics of transesterification of soybean oil”, Journal ofthe American Oil Chemists' Society, 74, 1457-1463, (1997)). These rateconstants were calculated from experiments performed in a 1500 mL glasscylindrical reactor equipped with a mechanical stirrer. The rotationalspeed at which the measurements were conducted was 300 RPM and theauthors claim that at this speed, the mass transfer limitations aresignificantly reduced, and that the kinetic rate constants were measuredafter the mixture became homogeneous and are therefore intrinsic.

The reported rate constants for each reaction are tabulated below inTABLE 6. Here, the reaction network is considered to be serial, i.e.,triglyceride (TG) to di- (DG) to mono- (MG) to glycerol (G). The surfacerate constants were obtained by conversion from the homogeneous rateconstants reported by Nouredinni and Zhou (1997).

TABLE 6 Reaction Rate Constants For Biodiesel Reaction NetworkHomogeneous rate constant Surface rate constant Reaction (L/(mol-s))(m⁶/(mol-m² _(bubble)-s) TG ^(→) DG 0.05 7.569 × 10⁻⁹ DG ^(→) TG 0.1101.665 × 10⁻⁸ DG ^(→) MG 0.215 3.255 × 10⁻⁸ MG ^(→) DG 1.228 1.859 × 10⁻⁷DG ^(→) G  0.242 3.663 × 10⁻⁸  G ^(→) DG 0.007 1.060 × 10⁻⁹

The six reactions were then simulated as a set of ordinary differentialequations in MATLAB and the time required for the weight fraction ofFAME to increase to 60% by weight was calculated. This procedure can berepeated for every value of droplet radius in order to obtain a mappingof the time required for the transition to a homogeneous reaction as afunction of the droplet radius. TABLE 7 sets forth the calculated timesrequired for the two extreme droplet radii.

TABLE 7 Heterogeneous reaction time for different droplet radii Dropletradius (m) Time (s) 50 × 10⁻⁹ 0.003 10 × 10⁻⁶ 1.16Of note, this model uses kinetic rate constants that were measured at50° C. and at a catalyst concentration of 0.2% NaOH. If differenttemperatures or catalyst concentrations are to be used, then the rateconstants must be adjusted accordingly.

From the results of the kinetic model and the hydrodynamics within thedisclosed apparatus/system, the following conclusions are reached:

-   -   Due to the intense mixing in the interaction zone, small        droplets of methanol are formed and dispersed in the soybean oil        phase.    -   The very large interfacial area provided by these small droplets        tremendously enhances the mass transfer rates, and the initial        lag time is significantly reduced. The transition to the        homogeneous reaction is hence accelerated.    -   Once the reaction becomes homogeneous, the reaction is limited        by the solubility of methanol in the FAME-enriched vegetable oil        phase. The glycerol has very low solubility in the oil phase and        hence remains as a separate phase. Methanol partitions between        the glycerol phase and the FAME-enriched oil phase.    -   The flow regime prevalent downstream from the microreactor is        significantly different from the intense backmixing (as in a        Continuous Flow Stirred Tank Reactor (CFSTR) emulator) at that        point and approaches that of a system without further mixing in        the flow direction (as in a Plug Flow Reactor (PFR) emulator).        This behavior should help minimize droplet coalescing, thereby        allowing continuous diffusion of glycerol to the droplets and        methanol from the droplets into the oil phase until desired for        downstream processing demands.        Based on the foregoing, it is believed that it would be possible        to conduct a biodiesel reaction in two stages:    -   Initially, pass the mixture through a high shear device, so that        there is significant interfacial area enhancement and the        initial lag is reduced. The transition to homogeneous reaction        can be achieved in a very short time in such a device    -   Once the transition to the homogeneous reaction phase is        accomplished, the mixture can be passed through a PFR so as to        allow the reaction to proceed to its equilibrium conversion.

This hypothesis has been evaluated with reference to data reported inthe literature [e.g., Costello, “Summary Tube in Tube (STT) Reactor,”Kreider Laboratories, Camarillo, Calif. (2006), Zhou and Liang (2006),Boocock, et. al. (2000), Ma and Hanna (1999), and Noreddini and Zhou(1997)]. Indeed, the data in the literature clearly indicates massaction kinetics are in operation at “long times”. Of note, the rate canbe expected to drop off as conversion increases. Consequently, acontinuous system should operate with maximum mixing early toeliminate/reduce mass transfer resistances, as in a CFSTR emulator, andto drive the reaction to completion in a PFR emulator, therebyeliminating the potential detrimental effects of back-mixing in thelater stages of the reaction (i.e., at high conversions). Also, thetransition from the heterogeneous to the homogeneous regime (60 wt %FAME) can be expected to occur more quickly, as compared to the lagphase reported in the literature, which is in the range of 20-30 minutesin current large commercial vessels. Such commercial systems typicallyonly accomplish macro-mixing.

Process intensification systems: The micro-mixing produced by processintensification (PI) reactors has been reported to dramatically overcomemass transfer issues, and thus increase reaction rates for biodieselformation (Costello (2006)). Using a spinning tube in tube (STT)reactor, it is claimed that production is done at a residence time of0.5 seconds due to the high shear field producing large interfacialareas. Furthermore, since the mass transfer is enhanced significantly,the glycerol formed in the FAME-oil phase is transported to the otherphase quickly, resulting in improved product quality. It is furtherclaimed that the FAME-oil phase retains less than 0.05% and thus lessdownstream processing is required.

These reported results support the concept that successful scale-up canbe accomplished by holding shear constant. Consequently, any device thatgenerates high shear will be effective in accomplishing favorableresults. Exemplary systems include the Shockwave Power Reactor(HydroDynamics, Inc., Rome, Ga.), and in general all types of SpinningDisk Reactors, plus microchannel reactors (Velocys, Plain City, Ohio).The disclosed apparatus/systems also achieve desired high shear byutilizing microreactor designs/geometries to obtain micro-mixing time atscales of 1-4 μs. Residence times of 0.5-1 ms are obtained with thedisclosed apparatus/system in the reaction chamber where energydissipation rates readily form droplets in the 25-500 nm range.

The results set forth in the literature confirm that RPM is an importantvariable. Of note, due to insufficient data, energy modeling is not ableto accurately predict the size of a methanol droplet. The predictedvalues are on order of 50 nm. In order to estimate how close this valueis to the droplet sizes reported by others in the literature, aqualitative assessment was made by analyzing the phase separation timefor a glycerol droplet in FAME and comparing such phase separation timeto experimental observations. Several assumptions were made tofacilitate this calculation:

-   -   1. The viscosity of the organic phase was that of pure FAME. In        the experiment, the actual phase was a combination of methanol        and FAME.    -   2. The height of the liquid in the sample jars from the        experiments was on average 15 cm.    -   3. The droplets moved at the terminal velocity and did not        coalesce. This assumption permits use of Stoke's Equation.        For a sphere with radius R_(p) moving at its terminal velocity,        Stoke's Equation gives:

6πμUR_(p)=V_(p)gΔρ

where μ=viscosity of the continuous phase (μ=2.5E-3 kg/m/s for FAME);U=velocity of droplet [m/s]; R_(p)=radius of droplet (R_(p)=50 nm);V_(p)=volume of droplet (V_(p)=5.24E-22 m³); g=gravity constant (g=9.81m/s²); and Δρ=difference in density between droplet and continuous phase[(1,280−880)kg/m³=400 kg/m³].

Solving for U:

$U = {\frac{V_{p}g\; \Delta \; \rho}{6\; \pi \; \mu \; R_{p}} = {{2.8\; E} - {7\mspace{14mu} m\text{/}{s.}}}}$

Solve for the settling time:

$t = {\frac{H}{U} = {\frac{0.15\mspace{14mu} m}{{2.78\; E} - {7\mspace{14mu} m\text{/}s}} = {{536\text{,}697\mspace{14mu} s} = {6.2\mspace{14mu} {days}}}}}$

Although this time represents the time required for droplets to movefrom the top to the bottom of the mixture and also ignores coalescence,it does provide useful data from an order of magnitude perspective andmay be compared to actual observations and far exceeds actual datareported in the literature.

Example 5 Experiments to Determine Mass Transfer Characteristics andParameters

The interfacial area in process intensification equipment can bequantified by performing mass transfer studies. In particular, a soluteis introduced into the system of interest (e.g. methanol and soybeanoil) and the mass transfer rate of this solute from one phase to theother is measured. The interfacial area can then be calculated. In orderto accomplish this determination, it is necessary to have an estimate ofthe mass transfer coefficients in the individual phases—which can bedetermined through bench-top experiments.

Calculation of Mass Transfer Coefficients:

a) Continuous mixing of both phases: In the setup schematically depictedin FIG. 21, both the organic and aqueous phases are agitated to ensureback-mixing of both phases. From this experimental technique, the valueof the overall mass transfer coefficient of the phase of interest can beobtained.

b) Mixing of one phase: With reference to FIGS. 22A and 22B, a set oftwo experiments may be conducted in which one phase is agitated, i.e.,one phase is well mixed, and the other phase is maintained as a stagnantphase. This phase can hence be considered as a sheet and the diffusionallength in this phase is the thickness of the phase.

By solving the partial differential equation for the gradient in thestagnant phase, the diffusion coefficient in that phase can becalculated. With the knowledge of the diffusion coefficient, the masstransfer coefficient for the phase can be obtained:

$k_{l} = \frac{D_{A}}{\delta}$

where k_(l)=mass transfer coefficient (m/s); D_(A)=diffusion coefficientfor Phase A (m²/s); and δ=thickness of the stagnant layer (m).

The same procedure may then be repeated for the case where thestagnant/agitated phases are reversed (FIG. 22B). From this experiment,the mass transfer coefficient for the second phase can be obtained.

c) Verification of mass transfer coefficients: An experiment to verifythe obtained mass transfer coefficients may then be performed. Withreference to the schematic depiction of FIG. 23, both phases arestagnant and hence the diffusional length in both phases is known. Bysolving the partial differential equations for concentrationsimultaneously, the diffusion coefficient in each phase can be obtained.With this, the mass transfer coefficients can be obtained and comparedwith the values obtained in the previously described experiments. (See,generally, Crank, J., “The mathematics of diffusion”, Oxford UniversityPress, 1975; and Carslaw, H. S., Jaeger, J. C., “Conduction of heat insolids”, Oxford University Press, 1959.)

Calculation of interfacial area: Reactant systems may be processed inthe disclosed apparatus/system and a measurement of inlet concentrationof the solute is made. The system is run at different flow rates untilthe concentration at the outlet is equal to the equilibriumconcentration. The residence time is measured for this run and, hence,the rate of mass transfer can be calculated. The interfacial area canthen be obtained.

Data from two systems were obtained using this approach: (a) the soybeanoil-MeOH system, and (b) the transfer of aspirin from an octanol phaseto a water phase. In both cases, the estimated diffusion coefficientswere in the range 1-5×10⁻⁹ m²/s and interfacial transfer coefficients ashigh as 0.5 m/s. Using these parameters and assuming it takes the entireresidence time in the disclosed interaction/reaction chamber (0.5 to 1.0ms) to reach equilibrium, droplet sizes (i.e., radius) in the range of100-200 nm will be sufficient to accomplish the desired transfer amount.

Example 6 Production of Polymer Matrix/Chaperone Systems

Exemplary nanosized polymer particles were generated using two methods:(a) emulsion-evaporation, and (b) precipitation.

Emulsion Method

The emulsion method is a “top down” method that involves formation of astable emulsion of a polymer/solvent solution with an immisciblenon-solvent liquid and subsequent removal of the solvent. For sometests, an API (carbamazepine) was added to the solvent phase to beincorporated inside the polymer particles. A nano-emulsion was formed byfirst preparing a coarse emulsion with the solvent and aqueous streamsusing an IKA T-25 high shear mixer, then processing with aMicrofluidizer® processor. The nanoemulsion size was controlled byvarying the processing pressure, the number of passes and theconcentration of the oil phase. The solvent was then removed from theemulsion, leaving only the polymer particles suspended in the waterphase.

In an exemplary application, poly(lactic-co-glycolic acid) (PLGA)particles were formed. The polymer was dissolved in dichloromethane(DCM) at concentrations between 10 and 80 mg/ml. The solution was thenmixed at concentrations of 1-10% dichloromethane with water thatcontained poly(vinyl alcohol) (PVA) to form a coarse emulsion. Theprocessing pressure was varied between 70 and 140 Mpa and some materialwas subjected to multiple passes. All tests were performed on a M-110EHMicrofluidizer® processor with a F20Y (75 μm)-H30Z (200 μm) chamberconfiguration.

The solvent was then removed using several different methods that havedifferent driving forces to obtain particles with different sizes. Anevaporation method was performed in a “rotovap” at 25 kPa absolute for10-20 minutes, depending on the concentration of the dichloromethane.The temperature of the sample was maintained at room temperature using awater bath. A co-solvent extraction method was performed by mixing theemulsion with a co-solvent immediately after processing. The co-solventdoes not dissolve the polymer, but is miscible with the water phase andorganic phase.

Precipitation Method

The precipitation method is a “bottom up” process that involvesprecipitation of polymer from a solution by adding apolymer/solvent/(API) solution to a miscible anti-solvent. Addition ofthe anti-solvent causes the polymer to become supersaturated andprecipitate out. These streams were mixed inside an interaction chamberat various shear rates by controlling the orifice size and processingpressure.

A surfactant was added to the anti-solvent (water) in order to: (a) tostabilize the nanoparticles and limit their growth, and (b) to minimizeagglomeration of the particles and thereby create a stable suspension. Anon-ionic surfactant was used, Solutol® HS 15 (polyoxyethylene esters of12-hydroxystearic acid; Bayer).

Nanosuspensions of two different polymers, poly(epsilon-caprolactone)(PCL) and poly(D,L-lactide-co-glycolide) (PLGA) were produced using theprecipitation method. These polymers were dissolved in acetone atconcentrations ranging from 10 mg/ml to 40 mg/ml. These solutions weremixed with water that contains a surfactant with flow ratios in therange of 1:2-1:10. Process pressures were varied between 35-140 mPa.

Drug Encapsulation

To date, there have been only qualitative measurements of the amount ofdrug that was encapsulated within the polymer nanoparticles during theforegoing tests. A qualitative test was performed by performing tworeplicate tests, both with the same concentrations of API, one with thepolymer and one without polymer. These samples were analyzed usingoptical microscopy to identify any large drug particulates.

Particle Size Analysis

The particle size distribution of these samples was measured using aMalvern Zetasizer® instrument which uses dynamic light scattering. Thesamples were measured at 25° C. with water as the continuous phase andPLGA as the particle phase. The reported results are the Z-Average,which is a volume weighted average.

Electron Microscopy

Two different electron microscopy techniques were employed. The emulsionevaporation samples were analyzed using a transmission electronmicroscope (TEM) (Model JEOL, JEM 1010 TEM) operated at 60 kV. Astaining material was used to increase the contrast of the particles.The samples prepared using the precipitation technique were analyzedusing a scanning electron (SEM) (Hitachi S-4800 FESEM).

Light Microscopy

To determine if the API was encapsulated within the polymer particles,the samples were analyzed using a light microscope. Although lightmicroscopy is not able to achieve resolution at the nanoparticle scale,it is powerful enough to see preliminarily whether the API has beenencapsulated.

Results

Results from the processing of the polymer nano-particles using theemulsion method are set forth in Table 8.

TABLE 8 C PLGA Pressure # of Co-Solvent # (mg/ml) % DCM (MPa) PassesEvap. (nm) (nm) 1 10 5 70 1 223 129 2 10 5 70 2 100 76 3 10 5 70 3 11499 4 10 1 70 1 3254 124 5 10 10 70 1 168 116 6 10 5 105 1 127 84 7 10 5140 1 140 149 8 40 5 70 1 193 146 9 80 5 70 1 168 119

All of the emulsion tests were performed with 1% PVA dissolved in thewater phase to stabilize the emulsion. The concentration of the PLGA inthe DCM is designated as “C PLGA.” The amount of oil phase that is mixedwith the water phase is shown as “% DCM.” The processing pressure isshown as “Pressure.” The Z-average particle size for the two differentsolvent removal techniques are shown as “Evap.” for the solventevaporation technique and “Co-Solvent” for the co-solvent extractiontechnique.

FIG. 24 is a TEM image of particles formed using the emulsion method(sample #9). The black specks that are shown in the image are identifiedas the contrast agent, phosphotungstic acid, which was used to enhanceimaging.

Results from the processing of the polymer nanoparticles using theprecipitation method are set forth in Table 9.

TABLE 9 % C Poly. Shear Z-ave. # Polymer Acetone (mg/ml) (s⁻¹ × 10⁶)(nm) 1 PCL 10 20 1.2 445 2 PCL 10 20 1.2 517 3 PCL 10 20 6.0 281 4 PCL10 40 6.0 341 5 PCL 10 10 6.0 258 6 PCL 10 20 6.8 280 7 PLGA 10 20 6.0230 8 PLGA 9 10 6.8 184 9 PLGA 17 10 6.8 173 10 PLGA 25 10 6.8 177 11PLGA 33 10 6.8 212

All of the precipitation tests were performed with 1% Solutol dissolvedin the water phase to stabilize the dispersion. The type of polymer usedis labeled as “Polymer.” The concentration of the polymer in the acetoneis labeled as “C Poly.” The amount of acetone that is mixed with thewater phase is labeled as “% acetone.” The shear rate, which is afunction of pressure and orifice size, is labeled as “Shear.” TheZ-average particle size is labeled as “Z-ave.” FIG. 25 is an SEM imageof particles formed via the precipitation method (sample #3).

Drug Encapsulation

Optical microscope images for drug encapsulation tests conducted hereinare set forth in FIGS. 26A and 26B. The samples used to generate theseimages were prepared under the conditions set forth in test #10 of theprecipitation method. FIG. 26A reflects a precipitation test run withboth polymer and API, whereas FIG. 26B reflects a test run with APIalone. The absence of API particles from the image of FIG. 26A indicatesthat the drug is encapsulated within the polymer, as opposed to the freecrystalline form of the API particle shown in FIG. 26B.

Conclusions

Polymer nanosuspensions in the range of 50-500 nm with two differentpolymers were successfully processed using both emulsion and theprecipitation methods as described herein. By controlling the processingparameters, nanosuspensions with various polymer sizes and densitieswere created.

For the emulsion method, the dispersions that were prepared byco-solvent extraction were, in general, smaller than those prepared bythe evaporation method. This may be due to the stability of the emulsionafter processing and/or agglomeration of the particles either during thedrying process or after drying. The co-solvent extraction process wasperformed immediately after processing. Some time (5-30 min.) elapsedbefore the evaporation technique was performed which may have enabledthe emulsions to ripen.

By varying the process pressure (70-140 Mpa) and number of passes (1-3),the size of the polymer particles varied in the range of 75-250 nm.Given a desired formulation, the particle size of the dispersion may becontrolled by selecting appropriate processing conditions. Based on theimages provided herein, encapsulation of the API within the polymernanoparticles appears to have been successfully achieved through thedisclosed techniques.

Although the present disclosure has been described with reference toexemplary embodiments and implementations thereof, the presentdisclosure is not limited by such illustrativeembodiments/implementations. Rather, the present disclosure is subjectto changes, modifications, enhancements and/or variations with departingfrom the spirit or scope hereof. Indeed, the present disclosureexpressly encompasses all such changes, modifications, enhancements andvariations within its scope.

1. A system for continuously processing at least two liquid feedstreams, comprising: a. a first feed pump that is adapted to pump afirst feed stream downstream at a controlled rate; b. a second feed pumpthat is adapted to pump a second feed stream downstream at a controlledrate; c. at least one intensifier pump positioned to receive the firstand second feed streams from the first and second feed pumps, theintensifier pump adapted to pressurize the first and second feed streamsto an elevated pressure; and d. a microreactor downstream of theintensifier pump, the microreactor adapted to effect high shear fieldsso as to achieve thorough mixing of the first and second feed streams.2. The system according to claim 1, wherein at least one of the firstfeed pump and the second feed pump is a peristaltic pump.
 3. The systemaccording to claim 1, further comprising a recycle feed stream that isintroduced to the at least one intensifier pump for combination with thefirst and second feed streams.
 4. The system according to claim 1,wherein the first and second feed streams are delivered to the at leastone intensifier pump in a coaxial arrangement.
 5. The system accordingto claim 1, wherein the microreactor is characterized by a geometryselected from the group consisting of: (i) a “Z” type single slotgeometry, (ii) a “Y” type single slot geometry, (iii) a “Z” typemulti-slot geometry; or (iv) a “Y” type multi-slot geometry.
 6. Thesystem according to claim 1, further comprising a cooling unitdownstream of the microreactor.
 7. The system according to claim 1,wherein at least one intensifier pump includes a plurality of spacedfeed ports, and wherein the first feed stream is introduced to the atleast one intensifier pump through a first feed port and the second feedstream is introduced to the at least one intensifier pump through asecond feed port.
 8. A system for controlling interaction ofconstituents at a nanoscale level, comprising: a. a first feed line forintroducing a first constituent to at least one intensifier pump; b. asecond feed line for introducing a second constituent to the at leastone intensifier pump; and c. a microreactor downstream of the at leastone intensifier pump, the microreactor adapted to effect nanoscaleinteraction between the first constituent and the second constituent;wherein the first feed constituent is delivered to the at least oneintensifier pump at a controlled rate relative to the secondconstituent.
 9. The system according to claim 8, wherein the firstconstituent and the second constituent are delivered to the at least oneintensifier pump so as to control mixing of the first and secondconstituents prior to pressurization by the at least one intensifierpump.
 10. The system according to claim 9, wherein controlled mixing isachieved by introducing the first constituent to the at least oneintensifier pump through a first port and the second constituent isintroduced to the at least one intensifier pump through a second portspaced from the first port.
 11. The system according to claim 8, furthercomprising a first feed pump for pumping the first constituent throughthe first feed line to the at least one intensifier pump.
 12. The systemaccording to claim 11, further comprising a second feed pump for pumpingthe second constituent through the second feed line to the at least oneintensifier pump.
 13. The system according to claim 12, wherein at leastone of the first and second feed pumps is a peristaltic pump.
 14. Thesystem according to claim 12, wherein the feed rates of the first andsecond constituents is controlled by operation of the first and secondfeed pumps.
 15. The system according to claim 8, wherein themicroreactor is characterized by a geometry selected from the groupconsisting of: (i) a “Z” type single slot geometry, (ii) a “Y” typesingle slot geometry, (iii) a “Z” type multi-slot geometry; or (iv) a“Y” type multi-slot geometry.
 16. A method for controlling interactionof constituents at a nanoscale level, comprising: a. feeding first andsecond constituents to one or more intensifier pumps at individuallycontrolled rates such that interaction is substantially prevented priorto pressurization within the one or more intensifier pumps; b.pressurizing the first and second constituents in a combined streamwithin the one or more intensifier pumps; c. delivering the combinedstream to a microreactor such that the first and second constituentsinteract within the microreactor at a nanoscale level.
 17. The method ofclaim 16, wherein the first and second constituents are fed to the oneor more intensifier pumps in feed lines that are coaxially aligned. 18.The method of claim 16, wherein the first and second constituents areintroduced to the one or more intensifier pumps through spaced portsdefined by the one or more intensifier pumps.
 19. The method accordingto claim 16, wherein the first and second constituents are fed to the atleast one intensifier pump through a first feed line and a second feedline that is coaxially positioned within the first feed line so as toprevent substantial mixing of the first and second constituents prior topressurization by the at least one intensifier pump.
 20. The method ofclaim 16, wherein the microreactor is characterized by a geometryselected from the group consisting of: (i) a “Z” type single slotgeometry, (ii) a type single slot geometry, (iii) a “Z” type multi-slotgeometry; or (iv) a “Y” type multi-slot geometry.
 21. The method ofclaim 16, further comprising recycling at least a portion of effluentfrom the microreactor to the one or more intensifier pumps.
 22. Themethod of claim 16, wherein the individually controlled rates fordelivery of the first and second constituents to the one or moreintensifier pumps are effected by individually controlled feed pumps forthe first and second constituents.
 23. The method of claim 16, whereinthe individually controlled rates are effective to control the ratio offirst constituent to second constituent fed to the one or moreintensifier pumps.
 24. The method of claim 16, further comprisingcooling or quenching the combined stream after interaction within themicroreactor.
 25. A method for controlled crystallization, comprising:a. delivering a solvent stream and an antisolvent to at least oneintensifier pump at a predetermined ratio; b. pressurizing the solventand the antisolvent in the at least one intensifier pump; c. feeding thepressurized solvent and antisolvent to a microreactor on a continuousbasis, the microreactor being effective to define a nanosuspension andeffect interaction of the solvent stream and antisolvent stream at ananoscale level; d. obtaining constituent nanoparticle crystals from thenanosuspension that define a median particle size.
 26. The method ofclaim 25, wherein the solvent stream is selected from the groupconsisting of dimethyl sulfoxide (DMSO), N-Methyl-2-Pyrrolidone (NMP),methanol, ethanol, acetone, dichloromethane, octanol and isopropylalcohol, and the antisolvent stream is selected from the groupconsisting of water, hexane and heptane.
 27. The method of claim 26,wherein the solvent stream is DMSO and nanoparticles of azithromycin areobtained at a median particle size of about 50-100 nm.
 28. The method ofclaim 26, wherein the solvent stream is DMSO and nanoparticles ofoxycarbazepine are obtained at a median particle size less than 1000 nm.29. The method of claim 26, wherein the solvent stream is DMSO or NMPand nanoparticles of loratadine are obtained at a median particle sizeof less than 500 nm.
 30. The method of claim 25, further comprisingcooling or quenching the nanosuspension after interaction within themicroreactor.
 31. A method for controlling a reaction, comprising: a.delivering a first reactant and a second reactant to at least oneintensifier pump at individually controlled feed rates; b. pressurizingthe first and second reactants in the at least one intensifier pump; c.feeding the first and second reactants to microreactor that is adaptedto effect interaction of the first and second reactants at a nanoscalelevel; d. adjusting reaction selectivity by controlling interactionbetween the first and second reactants prior to the nanoscale levelinteraction within the microreactor.
 32. The method of claim 31, whereincontrol of the interaction between the first and second reactants iseffected by limiting contact between the first and second reactantsprior to pressurization in the at least one intensifier pump.
 33. Themethod of claim 31, wherein the first and second reactants are deliveredto the at least one intensifier pump through spaced ports defined by theat least one intensifier pump.
 34. The method of claim 31, furthercomprising cooling or quenching the first and second reactants afterinteraction within the microreactor.
 35. A method for accelerating areaction, comprising: a. delivering a first reactant and a secondreactant to at least one intensifier pump at individually controlledrates; b. pressurizing the first and second reactants in the at leastone intensifier pump; and c. reacting the first and second reactantswithin a microreactor that is adapted to effect interaction of the firstand second reactants at a nanoscale level; wherein the first and secondreactants react at an accelerated rate due to enhanced surfaceinteraction between the first and second reactants within themicroreactor.
 36. The method of claim 35, further comprising cooling orquenching the first and second reactants after reaction within themicroreactor.
 37. A method for controlling polymorph production,comprising: a. delivering a first stream and a second stream to at leastone intensifier pump at individually controlled rates; b. pressurizingthe first and second streams in the at least one intensifier pump; c.contacting the first and second streams within a microreactor to effectinteraction of the first and second streams at a nanoscale level;wherein polymorph production is controlled through control ofoperational parameters associated with the microreactor.
 38. The methodof claim 37, wherein the operational parameters are selected from thegroup consisting of microreactor design, microreactor geometry, pressuregenerated by the intensifier pump, supersaturation ratio, solvents,antisolvents, temperature and combinations thereof.
 41. The method ofclaim 37, further comprising cooling or quenching the first and secondstreams after interaction within the microreactor.